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Authors TIMOTHY E. REINHARDT is a senior industrial hygienist, Radian Corporation, 11711

SE Eighth Street, Suite 200, Bellevue, WA 98005-3543; and ROGER D. OTTMAR is

a research forester, U.S. Department of Agriculture, Forest Service, Pacific Northwest

Research Station, 4048 Roosevelt Way, Seattle, WA 98105. Fulfills cooperative

agreement PNW 91-0031 between the USDA Forest Service, Pacific Northwest

Research Station, and Radian Corporation
Abstract

Summary

Reinhardt, Timothy E.; Ottmar, Roger D. 1997. Smoke exposure among wildland

firefighters a review and discussion of current literature Gen Tech Rep

PNW-GTR-373 Portland, OR U S Department of Agriculture Forest Service,

Pacific Northwest Research Station 61 p

This paper reviews and summarizes literature about smoke exposure and the

resulting adverse health effects among wildland firefighters Many studies have been

done on this problem between 1973 and 1995 Overall the data indicate that smoke

exposure at wildfires and prescribed fires is usually no more than an inconvenience,

but on occasion it approaches or exceeds legal and recommended occupational

exposure limits Management action is necessary to bring all smoke exposures into

compliance with occupational safety regulations

Keywords Fire, smoke, human health, occupational exposure, safety smoke

exposure

Overexposure to carbon monoxide and respiratory irritants is likely among firefighters

when direct control of fire is required and smoke production is intense Such overexposures are mostly brief events, but sometimes poor atmospheric dispersion or

rigorous work schedules cause hours or even days of unhealthful working conditions

Increased respiratory health problems have been measured in wildland firefighters

Small but statistically significant declines in lung function have been observed in a

number of wildland firefighters, across both workshifts and seasons More data are

needed to determine whether these losses are reversible

Smoke exposure data are limited in geographic scope and representativeness and

focus mostly on large Western U S wildfires or prescribed fires in the Pacific Northwest Data-collection efforts have been ill prepared for the mobility and responsiveness needed to capture smoke exposure during initial attack, as a result most studies

have obtained many duplicative measurements of smoke exposure during the latter

stages of fire suppression when smoke exposure is considered low Exceptions to

this have identified a limited but significant problem Smoke exposure is likely to be

the highest during initial attack, during direct attack of fires in high winds, and in

large-fire situations that suffer from poor atmospheric dispersion

Recommendations are made to develop smoke exposure management plans Health

surveillance is recommended to accompany exposure management Collection of

additional exposure data is recommended, but only for high-exposure situations

and in regions that have not been well represented in the data collected so far

The following items summarize the conclusions of this review

• There is a smoke exposure problem among wildland firefighters in the United

States, but it is a manageable problem, requiring control during about 5 percent

of the workshifts studied

• The hazards in smoke seem to be limited to respiratory irritants and carbon

monoxide, but these can reach unhealthful levels at both prescribed fires and

wildfires Other potential health hazards include crystalline silica, which is a poorly

characterized but potentially significant hazard during fire operations in dusty conditions, and exposure to benzene among firefighters exposed to gasoline fumes
• Acute smoke exposure is a more prevalent problem than the average exposure

during a work shift Acute exposures are common, but shift-average exposures

frequently comply with exposure limits because the brief periods of overexposure

are compensated by lengthy low-exposure periods within workshifts

• Small declines in lung function have been detected among firefighters, with statistically significant losses shown across both workshifts and fire seasons, it is

unknown whether the cross-seasonal losses are reversible, but limited evidence

suggests that they are

• Ambient windspeed is a key factor controlling smoke exposure potential, with

smoke exposure proportional to windspeed at both prescribed fires and wildfires

Prescribed burning at either extreme of the fuel moisture prescription also may be

associated with increased smoke exposure among firefighters

• The work task of an individual at a prescribed fire strongly influences smoke exposure Those workers holding the fireline (maintaining fire within firelines) and conducting direct attacks usually have greater smoke exposure than workers igniting

prescribed fires or mopping up Similar trends are indicated at wildfires

• High smoke exposures should be expected when firehnes must be maintained in

spite of smoke exposure, such as at wildland-urban interface fires or during prescribed burning adjacent to poorly defensible resources Overexposure to smoke

also may be associated with direct attacks when fires are small or slow moving or

when mechanized equipment allows attack at the head of a fire Smoke exposure

also may be high when heavy ground fuels support smoldering combustion

• Smoke exposure management should be implemented for all regions of the United

States, because overexposure to smoke likely is not limited to one geographic

region or fuel type Insufficient data have been collected to show any regional or

fuel-specific differences that may exist at either prescribed fires or wildfires

• To develop an accurate risk assessment of the consequences of smoke exposure,

demographic data need to be collected to assess firefighter career smoke

exposures

• Further health effect evaluations should include newly hired firefighters to determine

whether first-season lung function decline is greater than the small seasonal losses

documented among experienced firefighters

• Strategists for smoke exposure management may wish to consider the physiological

effects of carbon monoxide exposure among smokers already subject to impaired

blood oxygen transport, and whether those individuals are at greater risk of adverse

consequences from job-related smoke exposure

• Further collection of smoke exposure data should be an integral component of

smoke exposure management plans By routinely measuring smoke exposure with

real-time instrumentation, the recognition, documentation, and avoidance of acute

overexposures are more likely to occur Safety and health managers should meet

with the appropriate occupational safety regulatory agencies (such as the Occupational Safety and Health Administration) and propose the routine use of electronic

carbon monoxide dosimetry as a cost-effective alternative to comprehensive smoke

exposure monitoring among firefighters
• Research-level data collection is indicated only for regions such as the Southwest,

Southeast, and Northeast where data are sparse, and then only to determine

whether smoke exposure management is warranted for those areas Data collection

is recommended for high-exposure situations, such as initial attack, wildland-urban

interface fires, backfiring, and burnout operations, to improve the strength of interpollutant correlations for routine monitoring When a firecamp is established in

smoky inversion conditions, ambient air quality monitoring should be conducted

Finally, analysis of the crystalline silica content of stored particulate samples is

recommended based on limited data showing a potential health hazard

• Enough evidence has been gathered to begin developing and implementing

strategies for smoke exposure management Management plans that address the

possibilities of overexposure as indicated by the existing data are not likely to

require changes in strategy as a result of further monitoring, only in the scope of

application

Contents 1 Introduction

1 Objectives

1 History

2 Overview

3 Health Hazards in Smoke

3 Occupational Exposure Standards

4 Prescribed Fire

6 Prescribed Fire Literature

16 Prescribed Fire Summary and Data Needs

17 Slash Burning

21 Broadcast Underbummg

22 Other Activity Fuels

23 Natural Fuels

25 Wildfire Suppression

26 Wildfire Literature

45 Wildfire Summary and Data Needs

47 Initial Attack

49 Project Fires

53 Interface Fires

53 Regional or Specific Fuel Type Issues

54 Conclusion and Recommendations

56 Units of Measure

56 References
Introduction

Objectives

History

Smoke exposure among wildland firefighters is a concern of few outside the fire management community Only recently has it attracted attention from occupational health

specialists Within the fire management community, interest in smoke exposure has

steadily increased, but few have any knowledge about the scope of the problem

beyond their own first-hand experience This review is aimed at those who have some

experience with wildland fire

This review summarizes current knowledge of smoke exposure among firefighters,

identifies significant gaps in knowledge, and recommends strategy to fill those gaps

for agencies considering management of smoke exposure risks Resources include

published and unpublished data about firefighter smoke exposure, the occurrence of

wildfires and prescribed fires in the United States, and the strategies and tactics of

fire management Anecdotal knowledge from experienced firefighting professionals

was helpful in summarizing current developments in the field In many cases, the lack

of objective data about smoke exposure in various fuel types and fire situations

makes "expert knowledge" the only available source of reference Other than seeking

further corroboration, no evaluation was made of any bias that may exist in the

expert knowledge

Smoke exposure has been a recognized issue since about 1910, the beginning of

fire management in the United States, because smoke has always been recognized

as an irritant to firefighters Witness the implementation of bandannas, which have

been commonplace among firefighters since 1910 Although occupational safety

was a rudimentary concern back then, the workplace laws, and science have

evolved dramatically since Current concern with smoke exposure dates from the

early 1970s, when a few investigations into fatigue and injury among firefighters

hinted at smoke exposure as a contributing factor

The interest in the topic waxes and wanes with the severity of fire seasons and the

results of each new study Studies have been done by various groups, especially at

wildfires, with the scope of these studies mostly limited to a few components of smoke

and a few days of sampling Lack of grounding in industrial hygiene theory and practice has hampered some studies The largest study to date (in terms of samples collected) was done in the mid-1970s by the USDA Forest Service (Jackson and Tietz

1979) In spite of results that found significant overexposure to carbon monoxide

(CO, the primary known hazard in smoke at the time) details about factors controlling

the exposures were not collected, and the data were not collected so that acute

health effects could be examined, which may be the most important aspect of smoke

exposure Other studies have had the industrial hygiene capability but insufficient

understanding of the wildland fire workplace, how variable it was, what factors

coincide to result in overexposure to smoke, and what it would take logistically to

adequately characterize smoke exposure Many studies have suffered from the

vagaries of fire well-laid plans for research were useless when weather and fire did

not cooperate to produce the anticipated phenomena of smoke exposure

1
A comprehensive approach to assessing smoke exposure and the resulting adverse

health effects among firefighters was developed at a meeting of wildland fire agencies, physicians, industrial hygienists, and safety experts in January 1989 (Ward and

others 1989) in San Diego. Unfortunately, the multiple goals of the participants

resulted in an unwieldy proposal to Congress for a multimillion dollar assortment of

projects, in spite of heroic efforts to pare down unnecessary work and focus on what

was really necessary. Congress did not fund the proposed project, and the participants have not revisited the issue with any coordination

The National Wildfire Coordinating Group (NWCG) has been the only interagency

focus for concern about smoke exposure and firefighter health in the last decade.

Supported by a small amount of funding, NWCG has brought together interested

agencies, coordinated research needs, funded a few small projects, and maintained

a central brokerage of information about the health hazards of smoke, it produces

a widely read newsletter1 that summarizes recent results in smoke exposure, health

effects research, and exposure management.

Overview Wildland firefighters are workers Where they do their jobs, in the forest or on rangeland of America, is a workplace. Occupational safety regulations in the United States

apply to all workers in all workplaces to ensure that no one will be exposed to unsafe

or unhealthful working conditions. There is no exemption from these laws for emergency workers, or workers employed by a particular employer It is each employer's

responsibility to see that their employees' working conditions are safe.

There is a smoke exposure problem among wildland firefighters in the United States,

but it appears to be manageable. Industrial hygiene measurements of firefighter exposure to respiratory irritants and carbon monoxide (CO) at prescribed fires document

incidents exceeding OSHA (Occupational Safety and Health Administration) permissible exposure limits (Reinhardt and others 1994), and evidence points to similar

overexposures at wildfires. Firefighters occasionally report illness from exposure to

smoke—both acute, adverse health effects and chronic illness that they (or others)

attribute to smoke exposure. Anecdotal reports of overexposure to smoke are common at both wildfires and prescribed fires. Most experienced firefighters can attest

to incidents in which they or others suffered from exposure to smoke. Although acute

effects are well known, links between smoke exposure and morbidity or mortality are

equivocal at the present time.

Anecdotal reports are insufficient to develop policy in the United States. Managers

here need what is perceived as more solid information to allocate resources effectively. There are a wide variety of potential management strategies to select from;

however, to spend limited resources on an ineffective shotgun solution to an ephemeral problem is no wiser than ignoring the problem If personal protective equipment

is chosen unwisely, the cure may be worse than the disease, especially to firefighters

who already carry a heavy load of equipment, work at the upper limits of endurance,

and are subjected to extremes of heat and cold while they work to control a physical

phenomenon that can kill without warning.

1

 The Newsletter, 'Health Hazards of Smoke, is available

from the USDA Forest Service, Northern Region, Equipment

Development Center, Fort Missoula Bldg 1, Missoula, MT

59501

2
Health Hazards in Smoke

Occupational Exposure

Standards

Attempts to quantify smoke exposure invariably conclude that it is a limited problem,

insignificant most of the time but possibly harmful some of the time, every report reviewed here concludes that smoke exposure deserves further analysis This conclusion frustrates managers looking for solutions rather than more studies, but follows

from the extremely transient nature of the phenomenon At any given wildfire or prescribed fire attended by firefighters, it is almost axiomat c that someone will enjoy

fresh air while another is exposed to varying degrees of smoke Industrial hygienists

find it difficult to deploy their equipment on the right firefighter at the right time and

place to measure one of those transient smoke exposure episodes that firefighters

talk about "You should have been here yesterday" is a phrase too often heard

To begin to grapple with the smoke exposure problem is to first realize that firefighters

are a diverse lot, differing in age, physical health, lifestyle attitude, and work habits

This variability influences their susceptibility to adverse health effects from smoke

exposure. No less significant in determining the boundaries of the smoke exposure

problem are the great variety of smoke exposures possible within the diversity of the

wildland fire milieu

The principal known inhalation hazards among wildland firefighters have been summarized in detail (Reinhardt and others 1994) The identity of these hazards seem to

differ little between prescribed fires and wildfires, although certain activities, fuels, and

situations may elevate exposure to one or more components Briefly, the chief inhalation hazards are CO, aldehydes, and respirable particulate matter (PM3 5) and total

particulate matter (TPM), either of which may contain crystalline silica Crystalline

silica is not considered a smoke exposure hazard per se because it is not created as

a combustion product, however, as an inhalation hazard common to many dusty environments, crystalline silica must be included in any general discussion of smoke

exposure hazards among firefighters unless smoke is the sole source of the particulate matter And, conversely, crystalline silica can be a hazard in the absence of

smoke Of the aldehydes, formaldehyde (HCHO) and acrolein have been studied the

most, but many other low-to middle-molecular weight aldehydes also are present in

smoke. Benzene is a potential hazard, depending on work activity and the hazard

evaluation guideline selected Other chemicals in smoke seem less likely to pose a

significant health hazard, but the list could expand or contract as our knowledge of

toxicology and smoke exposure improves (Dost 1991)

Several evaluation guidelines exist for occupational inhalation exposures The

Occupational Safety and Health Administration sets legal permissible exposure

limits (PELs) for all Federal employees in the United States, and for all private

industry employees not under the jurisdiction of a state agency to which OSHA has

delegated authority for enforcement of occupational safety programs. Twenty-three

states presently operate designated state agencies, such as the California Occupational Safety and Health Administration (CAL-OSHA), and have legal jurisdiction over

state and private industry workers. The National Institute for Occupational Safety and

Health (NIOSH) advises OSHA on health hazards in the workplace and establishes

recommended exposure limits (RELs). The American Conference of Governmental

Industrial Hygienists (ACGIH) recommends threshold limit values (TLVs) for worker

safety

3
Each organization expresses the exposure limits for airborne pollutants via three basic

time-categories These categories of exposure limits are

• Time weighted average (TWA), an average concentration for a normal 8-hour day

in a 40-hour workweek, to which nearly all workers may be exposed for a working

lifetime without adverse effect

• Short-term exposure limit (STEL), a maximum concentration to which workers can

be continuously exposed for up to 15 minutes without adverse effect

• Ceiling (C) a concentration that should not be exceeded even instantaneously

A 'skin" notation for a particular chemical indicates that dermal absorption is an

important route of exposure that should be considered in management strategies

Table 1 summarizes present exposure limits for these inhalation hazards from

regulatory agencies and the most current (or proposed) guidelines from occupational

health organizations

At a minimum, all worker exposures in the United States must comply with either the

PELs or the applicable state limits For evaluation guidelines that more accurately

reflect current knowledge of health hazards, ACGIH and NIOSH recommendations

are appropriate

Prescribed Fire Broadly speaking, a prescribed fire is a wildland fire that achieves vegetation management goals of the responsible agency Prescribed fire has traditionally been most

widely applied to activity fuels (fuels altered by silvicultural activities), including timber

harvest residues and thinning residues Underbuming in tree plantations to reduce

wildfire hazard and maintain pine species is a major application of prescribed fire in

Southern States Piling biomass residues and burning under favorable conditions is a

common practice in many parts of the country In the last 15 years, prescribed fire in

natural fuels has been recognized as an important tool to maintain fire-adapted ecosystems threatened by fire-intolerant species unnaturally favored by decades of vigorous fire suppression Proposals for restoration forestry in the inland Western United

States depend on large increases in thinning, selective harvesting, and burning

(Mutch and others 1993)

Because prescribed fire includes such a great variety of fire situations, making generalizations about smoke exposure is difficult Exposure potential may be expected to

differ among different prescribed fire applications Prescribed fires in activity fuels

have different characteristics than prescribed fires in natural fuels Prescribed fire

ignitions may be scheduled or unscheduled, but scheduled ignitions predominate

Common to prescribed fire in general—and particularly to scheduled ignitions—is the

assumption of responsibility by the on-site fire manager (fire boss) to maintain control

over the prescribed fire This responsibility for control raises the likelihood of high

smoke exposure should the fire test the boundaries of control The conventional

wisdom is that a brief control effort conducted in intense smoke often can prevent a

large resource loss, even among fire managers concerned about smoke exposure,

this "pay a little now or a lot later" maxim justifies smoke exposure that may be

harmful

4
Table 1—Occupational exposure limits for inhalation hazards

Standard

OSHA Permissible exposure limits

NIOSH Recommended exposure limit

ACGIH Threshold limit value

CAL-OSHA

Acrolein Benzene CO HCHO

Parts per million

0 1 TWAa

1 TWA

3 STEL

1 TWA

3 STEL

1 TWA

3STEL

1 0 TWA

5 0 STEL-Cb

1 TWA

1 0 STEL-C

10 0 TWAd

(skin)

1 0

5 0 STEL-C

50 TWA

35 TWA

200 STEL

25 TWA

35 TWA

200 STEL-C

0 75 TWA

2 0 STELc

016 TWA

1 STEL C

3 TWA C

75 TWA

2 0 STEL

Particulate

matter

Crystalline

silica

Mg/m3

Respirable

5 TWA

Total

15 TWA

Respirable

3 TWA

Respirable

5 TWA

Respirable

Total

Respirable

0 05-0 1 quartz

a

 TWA = time weighted average

b

 STEL-C = short-term exposure limit ceiling

c

 STEL = short-term exposure limit

d

 American Conference of Governmental Hygenists 1996

A general breakdown of work activities may be made for prescribed fires First, some

sort of incendiary technique is used to ignite the biomass within the area (unit) designated for burning. Drip torches, fusees, Aluma-gel balls, helitorches, flamethrowers,

drip torches mounted on all-terrain vehicles, and aerial incendiary devices (Ping-Pong

balls) are all employed in specific situations.2 Ignitions by aerial and all-terrain vehicle

can burn more acreage per day than hand ignitions, and may be necessary to

achieve residue consumption targets when fuel moisture is high, however, the greater

rates of heat release associated with aerial ignitions can cause control problems from

unexpected fire behavior. A specific pattern of ignition is selected for each prescribed

fire, depending on the local conditions and objectives of the burn

2

 The use of trade or firm names in this publication is for

reader information and does not imply endorsement by the

U S Department of Agriculture of any product or service
When the unit is ignited, some personnel are usually assigned to "hold" the perimeter

of the unit where fire is expected to challenge control preparations—usually the downwind and uphill firelines The fuel adjacent to these lines often is ignited first in a lowintensity fire to provide a burned buffer strip before main ignition of the unit The

'holders' may be assigned to one location for some time, moved from one critical section to another, or just patrol the edges of the burn When spot fires erupt outside the

firehnes or the prescribed fire crosses the fireline in a "slopover," the holders conduct

direct attack, "hotspotting" (seeking out and controlling the spread of the hottest portions of the fire) the unwanted fire with direct control efforts that culminate in mop up

(extinguishing smoldering fuels after the flaming phase of a fire)

For many prescribed fires, escape potential or smoke management restrictions warrant mop up of the unit after the main fire has dwindled into the smoldering phase

Mop up involves digging up and turning smoldering duff and large-diameter fuels,

scraping off embers, and extinguishing residual fire with dirt or water

In all regions of the United States, prescribed burning at the wildland-urban interface

is increasingly common Concern about fire and smoke impacts on properties adjacent to the burn unit limits the margin for error Additional personnel often must be

used to maintain burn perimeters near private property When a fireline must be held

in spite of adverse conditions, firefighters can be exposed to significant amounts of

smoke

Prescribed Fire There is very little literature about smoke exposure at prescribed fires Only six

Literature studies were found as of June 1995, which resulted in the following papers Jackson

and Tietz (1979), Reinhardt (1989, 1991), McMahon and Bush (1992), Materna and

others (1992a), Reinhardt and others (1994), and Betchley and others (1995) These

resources provide the basic data about smoke exposure at prescribed burns In some

cases, more thorough discussions of the methods and results were found in the

unpublished project reports These data provide a reasonable base from which to

evaluate smoke exposure at prescribed fires

Jackson and Tietz (1979)—The first attempt at exposure assessment at broadcast

prescribed burns was documented in a 1979 project record by Jackson and Tietz

This study examined only CO exposure but included both wildfires and prescribed

fires Exposure sampling at nine prescribed fires in 1975 and 1976 relied on measurements of CO in end-exhaled breath (alveolar air) to calculate carboxyhemoglobin

(COHb) levels from Ringold's equation (Ringold and others 1962) Samples were collected in the morning before firefighters went to the fireline and again within an hour

of leaving the fireline Time worked at the fireline differed but was usually more than

8 hours Only data from nonsmokers were used because COHb levels in smokers

were a large source of variation in the results Quality assurance data were not reported Measurements at seven prescribed fires in 1975 found that 12 of 233 firefighters (5 percent) had COHb levels 5 percent, which implies that they suffered

overexposure to CO (the CO standard was intended to prevent COHb levels above

5 percent) In 1976, two prescribed fires were monitored At the first burn, 12 firefighters were monitored, and none had a COHb level >5 percent At the second burn,

15 of 20 (75 percent) of the firefighters had COHb levels >5 percent The first burn in

1976 was in light, discontinuous fuels and low windspeeds (<5 m p h ), and the

second burn was in heavy fuel loading and winds of 5 to 10 miles per hour The high

COHb levels at the second burn were attributed to heavy smoke exposure during a

1 5-hour direct attack of a slopover on the uphill side of the fire

6
The monitoring strategy could have biased the results of this study to underestimate

smoke exposure in certain circumstances This is because the biological half-life of

CO is around 4 hours If smoke exposure is at a maximum early in the workday,

COHb from peak CO exposures early in the shift could be mostly eliminated from the

body by the t,me COHb is measured at the end of the shift

McMahon and Bush (1992)—In 1988, smoke exposure was monitored at 14 prescribed fires in Georgia by McMahon and Bush (1992) This study was primarily concerned with assessing potential exposure to herbicide residues from prescribed burns

on sites treated with herbicides under "brown and burn programs Personal and area

monitors were used to sample for the herbicides imazapyr triclopyr, hexazinone, and

picloram Coincidental with the herbicide monitoring was personal-exposure sampling

for PM3 5 and CO by using filter and cyclone assemblies and passive diffusion tube

dosimeters, respectively The PM3 5 monitoring was done at a higher sample flow

rate (4 0 rather than 1 7 liters per minute) to enhance detection limits Some monitoring for herbicides and total particulate matter was conducted using area monitors

Spike recovery data (addition of a known amount of analyte to a sample to evaluate

accuracy of a chemical analysis) are reported for herbades and detection limits are

reported for all methods used Data for particulate matter sampling indicated good

precision between the area method and the personal PM3 5 method, but a 12-percent

lower collection efficiency was observed for the cyclones operated at 4 liters per

minute versus the standard flow rate No herbicide residues were detected in 140

smoke samples, despite sensitivities below 4 micrograms per cubic meter and spike

recoveries in the 66 to 105 percent range Breathing zone samples of PM3 5 ranged

between 0 2 and 3 7 mg/m3 (median 1 3 mg/m3) Sample durations ranged between

1 2 and 6 3 hours, depending on the acreage burned imedian 2 8 hours) About half

of the CO samples were above detection limits and were quantified as ranging between 6 and 30 parts per million (ppm)/hour, with the nighest value averaged over

1 7 hours Thus the highest concentration was calculated to be about 50 ppm The

CO and PM3 5 concentrations are in agreement with those measured by other researchers at low- to moderate-exposure prescribed burns (see discussion below) In

view of the lower collection efficiency of the PM3 5 method used, the PM3 5 concen

trations may be biased slightly on the low side

This study also reported good correlations between PM3 5 and CO, with r2 ranging

between 0 74 and 0 81 (McMahon and Bush 1992) The slope coefficients agree with

those reported by Reinhardt and others (1994) McMahon and Bush (1992) concluded

that the OSHA PEL TWA exposure limits for CO and PM3 5 are not likely to be exceeded, but a 200-ppm ceiling limit for CO could be exreeded as workers occasionally move through areas of thick smoke

Reinhardt (1989)—The pilot study by the USDA Forest Service, Pacific Northwest

Research Station (PNW), primarily examined smoke exposure among USDA Forest

Service firefighters at broadcast burns of timber harvest residues (slash burns) in the

Pacific Northwest (Reinhardt 1989) Three days of smoke exposure also were measured in northern California—at one prescribed fire in grass and during mop up at

two wildfires Some of the results from this study were published in 1991 (Reinhardt

1991), but the final analysis of the data was completed in the 1989 report Firefighter

exposure to CO, carbon dioxide (CO2), benzene, acrolein HCHO, and PM3 5 was

measured concurrently Worst-case exposures were largeted in this study, where

sampling was done on whichever firefighters were in the smoke rather than monitoring

7
specific firefighters regardless of conditions during the day Shift-average exposures

were not calculated in this study Peak exposure data from intense smoke exposure

episodes are comparable with other studies (Materna and others 1992a, McMahon

and Bush 1992, Reinhardt and others 1994), because each study used nonrandom

sampling for peak exposure measurements This exploratory project lacked a

thorough quality assurance program, thus the data must be considered provisional

although much of the pilot study data are probably accurate because the same

instruments or methods were used in the 1994 project (Reinhardt and others 1994)

which did have a suitable quality assurance design

Benzene exposure was found to be the highest among those lighting prescribed fires,

although few data were reported "Direct attack" (hotspotting) was identified as a highexposure work activity for all pollutants The mean CO concentration during direct

attack was 33 ppm, and the mean HCHO concentration was 0 37 ppm The study

concluded that "lighting" was a low-exposure activity, averaging 4 ppm CO and 0 07

ppm HCHO "Holding line" was identified as a high-exposure work activity, averaging

31 ppm CO and 0 46 ppm HCHO in this study Mop up exposures were relatively high

in this study, averaging 31 ppm CO and 0 17 ppm HCHO The high mean smoke exposures observed for the "holding line" and "mop up" samples could be an artifact of

the nonrandom sampling—mostly limited to significant smoke exposure in this pilot

study

The acrolein data from the pilot study are probably not accurate exposure measurements This is because inadequate chromatographic performance could have allowed

a coeluting acetone peak to cause a positive bias in the acrolein measurement The

acrolein measurements did not benefit from the recent method improvement whereby

total acrolein recovery is obtained by summing chromatographic results for acrolein

and the x-acrolein breakdown product (Reinhardt and others 1994)

These chromatography problems did not affect the formaldehyde data, however The

concentration of the calibration standard for HCHO in the pilot study was independently verified by the USDA Forest Service Intermountain Research Station, which provided at least one quality assurance check of the calibration for HCHO Peak levels

of exposure to HCHO in the pilot study commonly ranged between 1 0 and 2 0 ppm

over sampling periods lasting 30 minutes or more The greatest HCHO exposure

measured was 3 2 ppm for 26 minutes Although the bulk of the HCHO data in the

pilot study agreed with data representing moderate smoke exposure in the 1994 project, the peak HCHO exposures were substantially higher than those measured in the

1994 project (Reinhardt and others 1994) Possible exposure differences between

the two projects are discussed below The highest of these peak concentrations exceeded OSHA STEL limits for HCHO exposure, thereby reinforcing the principle that

smoke exposure management will have to address short-term exposures to respiratory irritants to ensure compliance with OSHA exposure limits

8
Some justification for the accuracy of the HCHO data is found in the CO data from

the pilot study, which also were higher than the 1994 results (Reinhardt and others

1994), about 20 percent of the CO samples were above 100 ppm, and they ranged

up to 218 ppm The pilot study used the same techniques and similar calibration procedures as the better documented 1994 study Further evidence of the accuracy of

the 1989 HCHO data were the similar slope and intercept coefficients for the regressions between concurrent HCHO and CO samples in both studies. The peak CO exposures exceeded the former OSHA ceiling limit of 200 ppm, thereby providing evidence that peak exposure to smoke can exceed exposure limits designed to prevent

acute, adverse health effects

Benzene sampling was not well executed in the 1989 study As a result, few exposure

data were successfully obtained, and some of those were fraught with reagent contamination and sample breakthrough problems. This clouds interpretation of these

results, which were about an order of magnitude higher than those found in the 1994

study (Reinhardt and others 1994).

The pilot study found high exposure to respirable particulate matter among firefighters

Many data were missing in the study because of sampling difficulties, but over 30

percent of the PM3.5 data were above 5 mg/m3 and ranged up to 20 mg/m3 The

slope of the regression between concurrent PM3.5 and CO samples also agreed with

the similar regression measured in 1994 (Reinhardt 1989), which suggests the PM3 5

data were accurate.

Ambient windspeed was considered a key factor controlling smoke exposure potentialsmoke exposure was greater at higher windspeeds. The study also identified fuel

moisture (or relative humidity) as a possible factor contributing to high smoke exposure. The study found that smoke exposure increased proportionately to fuel moisture content of the 10-hour timelag fuels (those with a diameter between 1/4 and 1

inch). A possible explanation for this observation was that at higher fuel moistures,

flaming combustion was poor and a strong convection column was not developed,

which allowed any ambient wind to overcome the column and push smoke into firefighters stationed downwind of the fire.

The 1989 study had one additional observation worth noting, although it could be

coincidental' The dominant fuel species at the unit was associated with differences in

smoke exposure. Hemlock-dominated (Tsuga sp.) sites had a greater exposure to

CO (and especially HCHO) than any of the other sites, which included Douglas-fir

(Pseudotsuga menziesn (Mirb.) Franco), ponderosa pine (Pmus ponderosa Dougl

ex Laws.), a single prescribed burn in grass, and two wildfires in northern California

chaparral and oak (Quercus sp.)-grass savannah (Reinhardt 1989).

The dearth of quality control information makes it difficult to evaluate method-induced

bias in the pilot study measurements, but subjectively high smoke exposures were

commonly observed at those burns. The 1989 study had some unique aspects that

may have contributed to the high smoke exposures measured First, some of the

burns with high smoke exposure had relatively thick duff depths Smoldering consumption of duff is an inherently inefficient process, with high emission factors for

CO and particulate matter (Ward and Hardy 1986) Second, some of the higher exposure burns were ignited when conditions were marginal, and subsequent winds

caused significant control problems. Windspeed data were obtained from the local fire

managers in the 1989 pilot study, those data showed a strong correlation with the

9
measured smoke exposure, as they did in the 1994 project The range of windspeeds

was about five times greater in the pilot study, but those were instantaneous or hourly

average readings, and the 1994 data were fire averages Although the data are not

directly comparable, the higher smoke exposures in the pilot study could be caused

by burning in greater ambient windspeeds Third, there is presently a muchdiminished timber harvest level in the Pacific Northwest For locations with concomitant reductions in burning acreage, this may allow fire managers to be more

selective and obtain ideal burning conditions that reduce the potential for smoke

exposure Finally, attitudes about smoke exposure seem to have changed since the

1989 pilot study, at least in the Pacific Northwest Even as recently as 1988, there

were many fire personnel who believed that smoke was rarely, if ever, hazardous In

1995, the belief that too much smoke exposure is bad is more widespread, there are

fewer fire personnel who do not consider smoke exposure to be a potential problem

in this region

Materna and others 1992a—This report summarizes observations of smoke exposure and lung function by the California Department of Health Services among firefighters at wildfires and prescribed fires in California Separate investigations were

performed in 1987, 1988, and 1989 Details of the sampling and interpretation of results are found in individual project reports, such as that for the 1989 season

(Harrison and others 1992) The 1987 and 1988 sampling occurred only at wildfires

and is discussed in "Wildfire Suppression" in this review, as are the results of the

1989 lung function testing

The 1989 sampling included 3 days of smoke exposure monitoring at broadcast prescribed fires in the Mendocino National Forest, California The exposure monitoring

consisted of breathing zone measurements of CO, PM3 5, respirable crystalline silica,

and selected aldehydes over sample periods of various lengths Standard NIOSH

methods were used Quality assurance data are not reported About 4 hours of each

8-hour workday were spent at the small (<6 acres) broadcast prescribed fires of

logging slash, with one unit hand-ignited per day with drip torches On the third day,

the firefighters conducted mop up of the previous burns

Smoke exposure monitoring at the prescribed burns indicated that all average exposures across workshifts were within the OSHA PELs The authors point out that

exposure during the partial-workshift sampling periods was observed to exceed the

PELs on several occasions, they felt it reasonable to assume that firefighters could

perform similar tasks for periods up to and beyond 8 hours Mean CO exposure

during the prescribed fires averaged 17 7 ppm at one fire, and 9 2 ppm at the second

fire, where a stronger convection column pulled smoke away from the firelines The

highest CO exposure of the entire study was observed at a prescribed burn—38 ppm

averaged over 2 5 hours (this exceeded the 35 ppm OSHA PEL in effect at the time)

Most PM3 5 exposures were below the OSHA PEL Respirable particulate exposure

averaged 1 15 mg/m3 at the prescribed fires, with one exposure of 5 1 mg/m during

mop up at a prescribed burn During the first burn, PM3 5 exposure averaged 1 50

mg/m3, but at the second burn the PM3 5 exposure was lower—0 81 mg/m3 Crystalline silica was detected in 5 of 21 PM3 5 samples analyzed (range 1 to 8 percent

silica) Four of these detectable silica samples were collected during mop up at prescribed fires or wildfires, and the fifth was obtained during the flaming phase of a

prescribed burn

10
Aldehyde levels generally were low Mean and peak aldehyde exposures were not

reported separately for the prescribed fires Determination of low-level aldehyde

exposures in this study was limited by the sensitivity of the measurement method

used, this was especially so for short-duration peak samples Some of the samples

were very close to the limit of quantification, the authors consider those results to be

semiquantitative The mean HCHO concentration from 30 samples at wildfires—and

presumably, prescribed fires—was 0 13 ppm The two highest HCHO exposures

were over 0 33 ppm for 3- to 4-hour-duration samples (it is not known if these were

obtained at prescribed fires) Furfural was detected in 25 of the samples, with a

mean concentration of 0 028 ppm and a maximum of 0 058 ppm This is well below

the OSHA PEL of 5 ppm and the ACGIH TLV of 2 ppm Acetaldehyde was detected

in 24 of the samples, exposure averaged 0 044 ppm with a maximum of 0 08 ppm

This is far below the OSHA PEL of 200 ppm, and the ACGIH ceiling TLV of 25 ppm

Acrolein was detected in a few samples, but analytical problems (chromatographic

resolution) precluded accurate quantification The authors estimate that the highest

acrolein exposure was no greater than 0 02 ppm

The average exposure levels for CO, PM3 5, and HCHO are in good agreement with

measurements from prescribed fires in the Pacific Northwest (Reinhardt and others

1994) However, the highest concentration samples obtained in this study are about

one-fifth of the peak concentrations measured in the 1994 Pacific Northwest study

Thus the range of smoke exposures measured is less than in the Pacific Northwest

This may be a real difference, but is more likely to be a result of the differences in

sampling protocol (sampling in the 1994 Pacific Northwest study differed because it

specifically targeted peak exposure events)

The results of the study by Materna and others (1992a) indicate that strong plume

development during the prescribed burn could result in lower mean exposure to CO

and PM3 5 than when a strong plume does not develop This agrees with the conclusions of the 1989 pilot study (Reinhardt 1989) The authors also found that exposure to PM3 5 (but not CO or HCHO) was higher during mop up (at two wildfires

and one prescribed fire) than during 2 days of prescribed burning when the flaming

phase dominated This contrasts somewhat with the results of the 1994 study by

Reinhardt and others, which found that PM3 5 exposure was intermediate during mop

up compared with tasks earlier in a prescribed fire The different conclusions may be

due to small sample size in this study, or because this study compared overall exposure between the days, while the conclusions in the Pacific Northwest study were

based on exposure differences between work activities

Interpollutant correlations were tested between CO and PM3 5 and between CO and

HCHO These correlations are important because if consistency in the equations were

demonstrated nationwide, fire managers could minimize routine monitoring and rely

instead on strong correlations to infer exposure to many components of smoke by

measurements of one or two The CO vs PM3 5 correlation was moderately strong,

with an r2 of 0 6 The CO vs HCHO correlation was less strong, with an r2 of 0 45

The regression equations were not provided for comparison with the 1994 Pacific

Northwest results The correlation coefficient for CO vs PM3 5 is comparable to that

in the Pacific Northwest study The correlation coefficient for CO vs HCHO is much

lower than that in the Pacific Northwest study (Reinhardt and others 1994) This may

11
be a result of the difference in HCHO detection limits between the aldehyde analysis

methods in the two studies, rather than a poorer relation between the compounds A

lower detection limit results in less variability in HCHO measurements, especially at

lower concentrations This lower variability in turn reduces the variation in the correlation, thereby giving a better r2

 A poorer relation between pollutants is also possible

when other pollutant sources impact the firefighters, as would occur in urbanized

settings

Reinhardt and others (1994)—The 1994 cooperative study by PNW and Radian

Corporation monitored exposure to smoke among firefighters at prescribed burns

(Reinhardt and others 1994) Sampling used only personal breathing zone measurements to assess smoke exposure Pollutants concurrently measured included acrolein

and HCHO with EPA method TO-11 (U S Environmental Protection Agency 1984),

benzene with NIOSH method 1501 (National Institute for Occupational Safety and

Health 1989), CO and CO2 with Intersociety Committee method 128 (Lodge 1989),

and PM3 5 with NIOSH method 0600 (National Institute for Occupational Safety and

Health 1989) Firefighters were selected for sampling by random draw, and detailed

observation of them was done throughout their workday to discern differences in exposure among various work activities as well as compute TWA exposures A comprehensive quality assurance program was integrated into the study, a key component

absent or undocumented in other projects

Quality assurance data collected during the project indicated that the overall accuracy

of the exposure measurements (measured by percentage of recovery) was good for

CO and CO2 (100±8 and 3 percent, respectively) and acceptable for benzene

(100±26 percent) and for measurements of HCHO and acrolein (100±30 and 36 percent, respectively) Overall precision estimates (measured by relative standard deviation of field replicates) ranged between 14 percent for CO2 and 25 to 35 percent for

benzene, acrolein, CO, and respirable particulate, and up to 45 percent for HCHO

Exposure data were collected from 221 firefighters during 39 prescribed fires Workshifts averaged 11 hours, and about 7 hours were spent on-site during the burns The

study concluded that average exposure to smoke per workshift exceeded PELs for

respiratory irritants and CO for 1 to 5 percent of the firefighters The estimate of overexposure increased to 10 percent when the more restrictive ACGIH TLVs were used

as evaluation criteria The 1994 project found that smoke exposure was higher during

the burns, but the unexposed time setting up the bums and traveling between the

duty station and the unit brought many shift-average exposures within workshift exposure limits Table 2 shows the mean and maximum TWA exposures found in this

study

The workshift overexposures to smoke were mostly caused by intense smoke exposure during line holding, line supervision, and direct attack activities, when peak exposures could exceed recommended STELs Smoke exposure was lowest for the fire

lighters and burn boss and during mop up Table 3 shows the differences in mean

smoke exposure among various work activities

12
Table 2—Time-weighted average exposures by pollutant, Pacific Northwest,

1994

Pollutant

Acrolein (ppm)

Benzene (ppm)

Carbon dioxide (ppm)

Carbon monoxide (ppm)

Formaldehyde (ppm)

Respirable particulate (mg/m3)

Respiratory irritants (no units)

Durationa

Shift

Fire

Shift

Fire

Shift

Fire

Shift

Fire

Shift

Fire

Shift

Fire

Shift

Fire

Mean

0 009

0015

0016

0 028

450

519

4 1

69

0 047

0 075

0 63

1 00

04

06

Maximum

0 06

0 098

0 058

0 086

740

860

38

57

0 39

0 60

69

105

34

5 1

a

 Shift = entire workday fire = portion of workday on firelme

Table 3—Mean smoke exposure by work activity and pollutant, Pacific Northwest, 1994

Pollutant

Acrolein (ppm)

Benzene (ppm)

Carbon dioxide (ppm)

Carbon monoxide (ppm)

Formaldehyde (ppm)

Respirable particulate (mg/m3)

Burn boss

0 031

0 021

508

59

0 077

1 32

Lighting

0 005

0 045

510

37

0 038

0 75

Holding

0018

0 021

565

11 6

0 127

1 56

Holding boss

0 030

0 026

577

132

0119

1 81

Sawyer

0010

0 091

700

142

0 346

2 93

Direct attack

0 062

0 041

762

33 2

0 464

4 04

Mop up

0012

0 020

499

92

0 091

0 75

13
Table 4 shows the mean and maximum smoke exposure during samples identified as

"peak" exposure samples Peak exposure data may be compared with STELs and

ceiling limits so long as the biasing effect of sample duration is considered (in variable

atmospheres, sample concentrations tend to decrease with increasing sample duration) Peak exposure samples were typically about 20 minutes in duration Thus the

peak smoke exposures approached and may have exceeded 15-minute STELs for

aldehydes and the ceiling limit for CO Electronic carbon monoxide dosimeter results

for CO showed that instantaneous peak smoke exposures often were higher than

levels in these integrated samples

Smoke exposure was proportional to ambient windspeed for the direct-attack work

activity The report concluded that overexposures often occurred during direct attack,

which is in agreement with Jackson and Tietz (1979) The study found strong correlations among the pollutants in smoke It suggested that large-scale monitoring for

smoke exposure within the Pacific Northwest Region could rely on CO measurements

and these interpollutant correlations to minimize the sampling burden A significant

detriment to this concept is the potential for overexposure to TPM from nonsmoke

sources, such as entrained dust Crystalline silica and TPM were not monitored,

although filters from the project are archived, should crystalline silica analysis be of

interest in the future3 Benzene exposure was found to be within PELs, but could exceed RELs, especially among personnel handling gasoline or operating gas-powered

equipment at the fires

The 1994 Pacific Northwest study identified fuel moisture (also indicated by relative

humidity) as a possible determinant of smoke exposure The 1994 study had more

data at lower fuel moistures than the 1989 pilot study, and a parabolic trend appeared

in the exposure data, smoke exposure appeared to be higher at either extreme of the

prescribed burning range (low and high fuel moistures), but low in the midrange

(Reinhardt and others 1994) This still supported the 1989 explanation of poor column

development at high fuel moisture, and the added evidence of high exposure at low

fuel moistures is explained by the common occurrence of control problems at fires in

low fuel moistures Fire control problems are less likely if ambient windspeeds are low

or the layout of the topography and resources at risk is conducive to control Additional data analysis could better quantify these relations

The authors recommended that the Pacific Northwest Region develop and implement

a comprehensive risk management strategy to identify workers at risk from smoke

exposure, conduct medical surveillance of worker health, and maintain all smoke

exposures below occupational exposure limits

3

 Material archived at the USDA Forest Service Pacific

Northwest Research Station Forestry Sciences Laboratory

4043 Roosevelt Way NE Seattle WA 98105 6497

14
Table 4—Peak smoke exposure, by pollutant, Pacific Northwest, 1994

Pollutant

Acrolein (ppm)

Benzene (ppm)

Carbon monoxide (ppm)

Formaldehyde (ppm)

Respirable participate (mg/m3)

Mean

0 071

0 064

54 3

0 468

7 00

Maximum

0 129

0 277

179 4

1 456

37 11

Betchley and others (1995)—This study by the University of Washington s Department of Environmental Health examined changes in lui g function and prevalence of

adverse respiratory symptoms in a group of Pacific Northwest firefighters in 1992 and

1993, on behalf of the USDA Forest Service (Betchley ind others 1995) The study

had both cross-season and cross-shift results, as we'i ^ some annual data The

cross-shift results are especially significant because tH population underwent smoke

exposure assessment during these workshifts as part * the Pacific Northwest prescribed fire study in 1994 (Reinhardt and others 1994 The cross-seasonal and

annual results also are discussed here, although the pxposure of the population to

wildfires must be noted as a contributing factor to smo><e induced health effects The

study measured forced vital capacity (FVC), 1-second jtced expiratory volume

(FEVi), mean forced expiratory flow during the middle naif of the FVC (FEF25 75) and

the prevalence of respiratory symptoms in 76 firefighters across their workshifts in

1992 and 1993, data were collected before, during ana after each workshift Personal

smoking history was considered in the data analysis i he respiratory symptoms were

evaluated by self-administered questionnaires Smokf exposure measurements were

concurrently taken by PNW scientists Correlation of the smoke exposure measurements with the respiratory symptoms and lung function i3 the subject of a separate

paper (Betchley and others 1995)

The cross-shift results showed small but statistically s gnificant mean individual declines in FVC, FEV1, and FEF25 75 between preshift and the midshift and postshift

tests Respiratory symptoms of sore throat and chest tightness increased significantly

during the same periods The authors note that these uross-shift losses of lung

function were correlated with the smoke exposures mp-*sured by PNW scientists

(Betchley 1994) Clearly, these results demonstrate a i nk between occupational

smoke exposure and acute loss of lung function and Averse respiratory symptoms

Although a small loss of lung function might not be considered a severe adverse

effect by some, others might consider any job-related impairment of off-duty abilities

to be unacceptable, no matter how temporary the effe^s

15
Prescribed Fire

Summary and Data

Needs

The cross-seasonal comparisons examined the occurrence of respiratory symptoms

and pulmonary function performance among 53 firefighters across the 1992 fire

season The results showed mean individual declines in FVC, FEV1, and FEF25 75

although FVC decrements were not significant across the season In spite of these

functional declines no significant changes in respiratory symptoms were detected

across the fire season The cross-seasonal pulmonary function declines were consistent with those noted in other studies among wildland firefighters, which are

discussed below in "Wildfire Suppression "

These firefighters worked an average of nine prescribed burns (range 1 to 25 burns)

and six wildfires (range 0 to 24) during the season studied The postseason testing

occurred an average of 2 5 months after the last smoke exposure of the season,

which prompted the authors to note that postseason recovery was not as rapid as

they expected Ten firefighters were followed at the beginning of the next fire season,

about 6 months after the end of the 1992 fire season At that time, all but one individual had recovered to the baseline 1992 pulmonary function levels The authors

recommend a longitudinal study to determine whether acute decrements in lung function cause long-term chronic effects as has been noted for urban firefighters

(Sparrow and others 1982)

Prescribed burns in activity fuels are likely to cause occasional overexposure to

smoke among firefighters, especially over short periods The known health hazards in

smoke are CO and respiratory irritants Crystalline silica may be a hazard, but this

can be assessed inexpensively by chemical analysis of existing filter samples

obtained from firefighters

The long-term effects of smoke exposure on health and pulmonary function are not

known Demographic data are needed to assess how firefighting careers may be expected to progress in the future, as cumulative career exposure determines the additional lifetime risk of many chronic adverse health impacts A smoke exposure management program incorporating demographic assessment with medical monitoring

could not only track the performance of smoke exposure management strategies but

also assess long-term health implications and help to identify individuals at increased

risk of adverse health effects

Overexposure to smoke is likely at prescribed fires in regions of the country other

than the Pacific Northwest, although the percentage of overexposures may differ by

fuel type, burn procedures, and region Brief exposures to high concentrations of

smoke are possible in any type of prescribed burning, mostly in the control of small

escapes, while overexposure to smoke during an entire workshift may be a less prevalent problem Further comprehensive characterization of smoke exposure during

broadcast burns of activity fuels is not recommended in the Pacific Northwest To

date, the limited data from exposure monitoring in the rest of the United States are

consistent with data from the Pacific Northwest Smoke exposure management strategies should be extended nationwide, or data should be collected to show why prescribed burns in certain fuel types and regions have no potential for overexposure to

smoke

16
Slash Burning Prescribed burns of timber harvest residues are widespread in regions where timber

production is important In recent years, burning prescriptions have evolved from

nearly complete consumption of biomass on a site to lighter burns that reduce fine

fuels and minimize consumption of large-diameter fuels Great skill is sometimes

needed to successfully meet burning prescriptions Depending on unit size, topography, adjacent resources at risk, and fuel moisture burning crews may range

between 2 and 30 workers In early spring conditions one or two people can ignite a

unit and be assured that humidity recovery will extinguish the fire overnight Conversely, in summer or early fall a similar site might require 15 people to hold firelmes,

and mop up of the unit might continue for a week

Smoke exposure during slash burns has been amply covered in the Pacific Northwest

by Jackson and Tietz (1979), Reinhardt (1989, 1994) and the University of Washington lung function study (Betchley and others 1995) The studies reach similar conclusions and are not contradictory in their exposure measurement results Together, the

results of these studies define a limited but consistent smoke exposure problem

during broadcast burning in Pacific Northwest timber harvest residues Smoke exposure at these burns ranges from inconsequential to substantial, depending mainly

on ambient wind, fuel moisture, and fire behavior

The 1994 Pacific Northwest project results gave numerical estimates of the probability of a given exposure (Reinhardt 1994). About 90 to 95 percent of the time,

the smoke exposure will be minor and well within recommended exposure limits

Site and weather factors come together in the wrong combination, however, about

5-10 percent of the time, when firefighters can experience significant smoke exposure,

as demonstrated by the COHb measurements in Jackson and Tietz (1979) and the

exposure data of Reinhardt (1989) and Reinhardt and others (1994) . All three reports

associate high smoke exposures with holding the line downwind from the unit and

direct attack of slopovers that escape the prescription Reinhardt and others (1994)

and Jackson and Tietz (1979) rely on a large number of samples to document the

relatively infrequent (< 10 percent) occurrence of overexposure to smoke at prescribed burns; smaller data collection efforts are likely to miss such events These reports show that smoke exposure (especially over brief periods) can exceed exposure

limits for respiratory irritants (acrolein, formaldehyde other aldehydes, and PM3 5),

and CO. The Pacific Northwest pilot study (Reinhardt 1989) adds valuable worst

case exposure data for CO and HCHO and provides additional estimates of the upper

end of the exposure range Measurements of the worst smoke exposures may not

yet be in hand, because many experienced firefighters have attested to exposures

that subjectively exceeded the highest exposure events that we have sampled in the

Pacific Northwest projects. This should not be surprising, because the Reinhardt

(1989) project showed that even an observer with a modest amount of experience

can visually estimate worsening smoke exposure, and capturing brief, high-intensity

smoke exposures has proven to be a very elusive task for researchers

17
Most individuals will experience eye and respiratory tract irritation in situations with

high smoke exposure Some may have more severe reactions than others, depending

on their predisposition to the effects of inhaled irritants The University of Washington

study has demonstrated small cross-shift and cross-seasonal declines in pulmonary

function among prescribed fire personnel (Reinhardt and others 1994) Such declines

are forecast from exposure to respiratory irritants The cross-shift declines were

associated with prescribed burning, but the cross-seasonal declines have not been

ascribed solely to prescribed burning The health implications of these declines remains to be proven Certainly they could be considered an adverse health effect, but

most people might not notice small (1-2 percent) declines in pulmonary function On

the other hand, college students who are top athletes in aerobic sports might not

agree that a percentage or two loss in a pulmonary function index is insignificant

Limited annual test data of Betchley and others (1995) suggest that the observed

declines are reversible given enough time

Time is an important issue in evaluating health impacts and establishing risk-based

occupational exposure limits The demographic makeup of various agencies may

differ and should be considered when evaluating career health risks from occupa

tional exposure Some believe that the size of the wildland fire workforce has peaked

in some agencies, and career fire personnel thus will not be able to work "on the

ground' for only 5 or 10 years before moving to a smoke-free administrative job, as

may have been the rule in the past (Linane 1995)

• Demographic data need to be gathered to assess how firefighting careers develop

and how that might define the smoke exposure history amassed during a working

lifetime

Although the significance of the adverse effects may be debated, the exposure data

and observations of adverse health effects provide evidence that CO and respiratory

irritant exposure exceed healthful levels and a smoke exposure management program

is warranted, at least for prescribed fires of timber harvest residues Several unanswered questions remain in the available data

• Are lung function losses among firefighters in their first season of firefighting

greater than losses in subsequent seasons?

• Are cross-seasonal losses cumulative, or do firefighters in the Pacific Northwest

regain their pulmonary function during the off-season, as indicated by limited data?

• Are some personnel especially sensitive to the respiratory effects of smoke

exposure, and can screening identify these people?

• Is crystalline silica present in the dust that firefighters inhale at prescribed fires?

The first three questions could be inexpensively answered through long-term pulmonary function and respiratory health data collection, which could be an integral part of

the medical monitoring recommended for the Pacific Northwest by Reinhardt and

others (1994) A well-designed medical monitoring plan could provide data to answer

the questions without incurring the costs of separate studies If adequate respiratory

protection is an accepted component of a risk management strategy, then further pulmonary function studies per se may not be worth pursuing On the other hand, much

of the data collection for medical monitoring should be an integral part of risk management, thereby allowing objective evaluation of the effectiveness of strategies to reduce

respiratory health impacts

18
The fourth question is important because excessive crystalline silica exposure in other

industries has been associated with nonreversible fibrogenic changes in lung tissue

that impair pulmonary function If the dust firefighters breathe contains significant

crystalline silica (the likely source would be entrained soil dust), respiratory protection

might be warranted in some circumstances regardless of the presence of smoke

There are no data on this issue for the Pacific Northwpst Materna and others (1992a)

have demonstrated a potential problem in northern California This question could be

inexpensively answered by crystalline silica analysis of a cross-section of the filters

already collected and stored by the Pacific Northwest 1994 project (see footnote 3)

The highest CO exposures found at these burns can be expected to increase

COHb beyond the 5-percent threshold that OSHA intended to meet with the former

35-ppm CO exposure standard The Jackson and Tietz (1979) measurements demonstrated this at prescribed slash burns, even after adjusting their results downward by

1 percent to correct for a possible bias from their algonthm for converting alveolar

CO to COHb (see Brotherhood and others [1990] in Wildfire Suppression" section,

below) The results of COHb measurements in smokers at wildfires should be of concern to those responsible for crew management Smokers can have 5 to 10 percent

COHb from cigarettes, inviting impaired judgment when fire-generated CO adds

another 5 to10 percent COHb Administrative controls to minimize CO overexposure

at prescribed fires should be developed and implemented in the Pacific Northwest

Region without further study

Whether exposure control strategies should be extended to other regions and agencies is a difficult question The cost of compliance with exposure limits is significant,

but so are the costs of further industrial hygiene surveys to evaluate the need Local

funding for either is unlikely without upper management commitment Managerial

attitudes about firefighter smoke exposure differ Some managers are content to

avoid the issue, some are convinced the problem is severe and the liability is unacceptable, some consider smoke exposure to be part of the job, and some adhere

to the maxim that there is no smoke exposure in their rpgion In some areas, there

may be very little prescribed burning of timber harvest residues Such regions may

find the cost of compliance negligible Regardless of the area of the country, prescribed burns in timber harvest residues are likely to have sufficient fuel loadings to

produce smoke densities comparable to the prescribed fire data from the Pacific

Northwest Region, and because prescribed burns will occasionally go awry, firefighters will be exposed to smoke during control efforts

The data from the Jackson and Tietz (1979) report fcr example are dated because

of improvements in prescribed fire techniques and practice, but in the absence of

more recent measurements, one could assume that smoke exposure at slash burns

in the Northern Region of the Forest Service is similar to that in the Pacific Northwest

Region This conclusion follows because the percentage of overexposures to CO in

the Jackson and Teitz study (about 5 percent) is the same as in the Pacific Northwest

Region Discussion with some prescribed fire experts in the Northern Region characterize the smoke exposure problem as limited to steep terrain where "holding" is

required on the uphill side (Thomas 1994) More than one expert in the Rocky Mountains notes that irritation from smoke is especially bad in prescribed burns of highaltitude spruce and subalpine fir, smoke at one prescribed fire in 1994 caused emergency hospitahzations among the line-holding crew (Hvizdak 1994) In such incapaci19
tating exposures, unusual emissions from burning specific fuels may be less of a

factor than the intensity of the smoke exposure, as similar incidents occur in other

regions (Betchley 1993)

The exposure data from Materna and others (1992a) include two small prescribed

slash burns in northern California The mean pollutant exposures noted at these

burns are similar to the data from Pacific Northwest Region, even though the data

set is small The highest exposures they measured are consistent with average peak

values from the Pacific Northwest In addition to the other pollutants, 5 of 21 PM3 5

samples from this project had detectible levels of crystalline silica, and at least one

was from a prescribed burn Although the authors did not document noncompliance

with PELs over entire workshifts, they did measure partial-shift exposures above occupational exposure limits If the frequency of high-exposure events in California is

similar to the Northern and Pacific Northwest Regions, we would not expect data from

only two prescribed fires to capture high-exposure events, which occur with 5 percent

frequency Thus the limited data for prescribed fire smoke exposure in California are

consistent with those from the Pacific Northwest Region Some experts in California

consider smoke exposure there to be similar to the results from the Pacific Northwest

it is not a problem until the prescribed fire goes awry, then direct attack may take

place in significant smoke (Stutler 1994)

In terms of annual acreage burned in prescribed fire, the Southeast leads other regions of the United States In spite of the volume of burning, there are few data to

conclude whether smoke exposure is a problem there Private industry and state forestry agencies conduct more prescribed burning in the South than Federal agencies

do The smoke exposure data of McMahon and Bush (1992) in southeastern broadcast burns are consistent with those from the Pacific Northwest The authors concluded that only the former OSHA ceiling exposure limit for CO (200 ppm) was likely

to be exceeded on those burns Their conclusion that TWA exposures were unlikely

to violate CO PELs is in accordance with observations in Pacific Northwest Region,

where less than 5 percent of CO exposures exceeded PELs and only 10 percent

exceeded more stringent recommended exposure limits (Reinhardt 1994) McMahon

and Bush did not consider additive effects on the same target organ from exposure

to more than one pollutant—the principal reason that the exposure limit for "respiratory irritants" was reached before the TWA PEL for CO in measurements within the

Pacific Northwest Region

McMahon and Bush (1992) and other observers note that smoke exposure seems

highest while firelines are being held and whenever direct attack of small slopovers

or spot fires is needed, an event occurring "approximately every couple of burns"

(Rounsaville 1994) As these are usually wind-driven events and the firefighters conducting direct attack would probably be in smoke from the unit being burned, shortterm exposures are likely to be the main problem requiring management These

events may be more frequent during growing season burns, when winds are more

erratic (Wade 1995) Finally, the prescribed burning season in the South is essentially

year round Should firefighters experience decreases in lung function, they may not

have sufficient unexposed time in a year to return to the functional baseline, as some

suggest occurs in populations where smoke exposure is more seasonal

20
In the Southwest, no data exist with which to assess smoke exposure One expert in

the Southwestern Region of the Forest Service concludes that there probably is not

much difference between the Southwest and the Pacific Northwest in terms of smoke

exposure at prescribed burns (Russell 1995)

• Because data from other regions either do not exist or are consistent with data

from the Pacific Northwest, exposure management should be extended to those

regions, or sufficient exposure measurements should be made to document the

compliance of their exposures during broadcast prescribed burning of timber

harvest residues

Broadcast Underburning Prescribed burning in surface fuels and the understory beneath a canopy of trees is

broadly termed "underburning " Variations of this practice result in specific names for

the general technique, such as hazard reduction burning, vegetation management

burning, and growing season burning It occurs widely especially in southern pine

plantations, and in pine and mixed-conifer stands thro ughout the South, Southwest

and interior West Proposals to apply restoration forestry in the inland Western United

States involve tenfold increases in thinning, selective harvesting, and burning (Mutch

and others 1993)

In the Southern Region of the Forest Service, 540,000 acres of Federal land are

treated annually by underburning (Rounsaville 1994) State and private forestry acreages in the Southeast are about an order of magnitude larger (Wade 1995) In most

of that Region, prescribed burning occurs in every month, reflecting a recent trend

toward more growing-season burning where burns traditionally were limited to fall and

winter months Growing-season burns now constitute oetween 15 and 50 percent of

the acreage burned in the Southeast, depending on the organization and location

(Wade 1995) Firehne personnel there are mostly permanent employees, a factor to

consider when estimating cumulative smoke exposure over a career and compared

with Regions more reliant on seasonal workers One observer estimated that a firefighter at a district having a good prescribed burning p'ogram averages 40 to 50 days

per year of prescribed fire, plus 30 days of wildfire suppression on the home district

plus another 20 days at wildfires in other Regions (Kubiak 1995) Underburning

is practiced to a lesser extent in the Great Lakes region comprising less than

10 percent of all prescribed burning in the Eastern Region of the Forest Service,

for example (Martin 1994)

One characteristic of underburning is that relatively low intensities often are prescribed

to avoid scorch damage to the overstory Such fires do not develop strong convection

columns, in contrast to broadcast fire techniques that generate higher fire intensities

to pull heat and smoke away from firehnes (Reinhardt 1989). As much as 40 percent

of the smoke emitted in a low-intensity fire is not entrained in the convection column

but is dispersed locally (Lavadas 1995) This local smoke may not contribute to

smoke exposure among fire lighters if they can stay ipwind of the fire, as is usually

the case. Holding efforts are often less extensive because the lower intensity fires

have less potential to cross firehnes (Hvizdak 1994) Many experts observe that

smoke exposure during underburning is normally highest for holding crews during

initial firing of the firehnes, when they might patrol in the smoke for an hour or so

(Rounsaville 1994), after which the smoke exposure is insignificant No measurements

are available to evaluate this, but the assertion of relatively low smoke exposure may

be accurate, especially for burns employing low-intensity backfire (planned ignition of

fuel ahead of a wildfire; one that burns into the prevailing wind) and flank fire ignition

21
patterns Others note that some jurisdictions have wildlife habitat trees to protect

within the burn unit, which requires close work in the smoke until the tree is secure

(Kubiak 1995) Ignition of prescribed fires from helicopters in the Southeast also may

be associated with limited smoke exposure if the aerial ignition is applied to larger

burns surrounded by secure firebreaks and roads, or the burns are unattended on

the ground

In parts of the Southeast, mop up and the associated smoke exposure may not occur,

especially where thin duff layers provide little available fuel and high humidity recovery

extinguishes burned areas overnight (Wade 1995) In units with a lot of stumps, mop

up may cause increased smoke exposures because of the many point sources within

the burned block The need for mop up may differ among organizations; some experts

perceive Federal land managers to be the most concerned with mop up to minimize

the impacts of residual smoke

Review of the literature shows very few measurements of smoke exposure among

firehne personnel conducting underburning in "activity fuels " Conspicuously absent

are exposure measurements during underburns in the South, Southwest, and Southeastern United States McMahon and Bush (1992) did not include underburning The

Reinhardt and others report (1994) contains exposure monitoring results from two

days of underburning in ponderosa pine stands in the interior of southeastern Oregon

Those burns (Dry Lake #1 and Dry Lake #2/Hogleg) were under relatively moist prescriptions Smoke exposure during those two days of burning was generally low,

although the sampling data were incomplete The worker most heavily exposed to

smoke during the two days was estimated to average 16 ppm CO and a combined

respiratory irritant index of 0 7 (based on OSHA limits) over 7 5 hours Interestingly,

this person spent most of the time operating an all-terrain vehicle with a mobile drip

torch Smoke exposure among the other personnel at the site averaged about onethird of this maximum, although sampling missed one key episode of direct attack on

a stopover where smoke exposure was probably higher This slopover was caused

by an unexpected wind shift that pushed fire outside the unit and required direct

attack

Similar small spot fires or slopovers occur frequently in underburns, perhaps every

few burns for a typical burning crew, according to one estimate of prescribed burning

in the South (Rounsaville 1994) Although topographical relief may be less in some

regions, which makes fire control easier, wind shifts can cause control problems anywhere Given the anecdotal reports of the frequency of small slopovers and spot fires,

and observations of smoke exposure during the initial burning out of the lines, the exposure problem in underburning activities is most likely compliance with short-term exposure limits rather than average exposure during the workshift The volume of prescribed underburning in the South, coupled with the lack of smoke exposure measurements, shows the need to obtain such measurements

• Data are needed to assess whether smoke exposures during underburning are

significantly different from broadcast burning in clearcut units, to determine whether

the practice can be categorically excluded from smoke exposure management

Other Activity Fuels Smoke exposure during certain types of prescribed fire in activity fuels may differ from

exposure situations reported in the literature Exposure assessment is warranted for

any prescribed burning with potential for excessive smoke exposure, if the existing

data are not considered representative

22
Chemically treated fuels ("brown and burn") are typically brush and young hardwood

species treated with herbicides months before prescribed burning occurs As mentioned previously, measurements designed to assess the exposure to herbicide residues were unable to detect herbicides in the smoke from such burns (McMahon

and Bush 1992) The production of other unusual combustion products has not been

evaluated If smoke exposure from brown and burn programs is of interest, an initial

step would be to review literature about toxic emissions from combustion of herbi

cides and herbicide decomposition products With detailed knowledge of the potential

hazards and estimated concentrations in emissions the need for further exposure

sampling could be addressed

Piling biomass residues by hand, tractor, or grapple and burning the piles at a later

date is commonplace in many parts of the country This practice may increase because of the desire to limit total emissions to the atmosphere from residue burning

Exposure measurements have not been made during pile burning but we can draw

on our own observations and the opinion of experts who conclude that exposure

during pile burning is unlikely to approach levels of concern because the convective

plume of the pile carries most of the smoke away from the firefighter (Russell 1995)

Natural Fuels Prescribed fires in natural fuels are either scheduled and ignited by natural resource

managers or result from lightning strikes The diversity of fuels and purposes of prescribed fire warrant examination of the exposure potential associated with each Prescribed natural fire (PNF) is lightning-caused fire aimed at accomplishing natural proc

esses within ecosystems Many agencies have increased or plan increases in PNF

within their jurisdictions, especially in wilderness and park areas Under the umbrella

of forest health, agencies in many regions of the United States also are planning for

a dramatic increase of scheduled ignitions in natural fuels Where PNF programs are

implemented, teams of fire behavior monitors may be assigned to check fire progress

through visual estimation of parameters such as flame length, rate of spread, and so

forth During first-hand inspection of the fire, these people can be briefly exposed to

significant amounts of smoke as they maneuver around the fire to check its progress,

but the exposure is usually minor (Kiefer 1995)

Chaparral—Chaparral poses a critical fire management problem in California and

parts of the Southwest Chamise (Ceanothus sp ) chaparral is an example of a fireadapted species where decades of fire suppression have resulted in aged stands with

a high proportion of dead fuels To reduce wildfire hazards in such fuels (especially as

the wildland-urban interface encroaches), fire is used to reduce fuel loading Some

times the fuels are crushed or otherwise treated before burning The flammability of

the fuelbeds can produce fires characterized by high fireline intensities and a high rate

of spread, especially in stands over 25 years old

The high proportion of extractable oils in the leaves of some chaparral species raises

a question about whether the smoke is particularly unhealthy Data addressing

unusual irritants or toxic compounds in the emissions from chaparral are not available Where unusual pollutants are suspected, better emission characterization in a

laboratory-scale setting might be the most efficient way to determine the hazard potential Once the combustion products are identified exposure measurements can

determine whether the pollutants reach hazardous levels in the breathing zones of

firefighters

23
No data are known that evaluate smoke exposures during prescribed burns in chaparral Emission monitoring over prescribed fires in southern California chaparral

showed that CO emission factors were only about half of those in logging slash (Ward

and Hardy 1989) Because CO correlates so well with other products of incomplete

combustion, it may be that exposure to CO and respiratory irritants are similarly reduced in chaparral burns Some smoke exposure occurs during hand-lighting of

chaparral burns, but the most smoke exposure is likely among holding crews (Smith

1995) Exposure during mop up is considered minimal in all but the oldest chaparral

stands because of the lack of residual fuel Either additional exposure assessment is

needed to prove there is negligible smoke exposure during chaparral burning, or exposure management strategies should be developed based on exposure measurements in other fuel types

Southern hardwoods—Prescribed burning in the "rough" is done as restoration

burning or maintenance burning throughout the South and Southeast Hardwood species and brush that flourish in the absence of fire are controlled by prescribed burning,

but smoke exposure potential may differ by organization conducting the burn Firefighters working for Federal agencies may have more smoke exposure than state or

private fire personnel because the Federal agencies may exert more effort in mopping

up burns to comply with smoke management goals (Wade 1995) Where roads and

natural barriers can be used as firelines, holding exposures may be brief, but some

land managers must contend with an encroaching urban interface or, conversely,

minimal-impact goals for wildlife areas, both of which can result in nonideal firelines

that require holding and patrolling (Seamon 1995) In these situations, smoke

exposure may be significant

Grasslands and sagebrush—Prescribed burning to maintain grasslands is common

throughout the United States and actually dominates prescribed burning in many

regions Grassland burning is characterized by high fireline intensities and rate of

spread This discourages firefighters from remaining in close proximity downwind from

the flaming front Smoke exposure is likely among fireline holders only at the beginning of the burn when fuels adjacent to control lines are burned (Romey 1994) When

fuel moistures are conducive to prescribed burning, the high flammabihty of grasses

and forbs results in relatively complete combustion and thus lower emissions of CO

and other products of incomplete combustion Prolonged exposure to smoke during

grass burns is unlikely, because there is virtually no smoldering after passage of the

flaming front

Prescribed burning in sagebrush (Artemesia sp ) is done primarily to replace the sagebrush with grasses and forbs for wildlife habitat Similar to chaparral and grasses,

sagebrush burns are very rapid with a strong flaming phase Smoldering combustion

is short lived, and smoke exposure is probable among lighting and holding personnel

only during ignition of fuel adjacent to downwind firelines (Linane 1995) The smoke

from sagebrush fires is very irritating (Linane 1994), and it may possess irritants or

special health hazards, but detailed characterization of trace emissions in the smoke

has not been done Emission sampling over full-scale prescribed burns of sagebrush

found that emission factors for CO and respirable particulate matter during the flaming

phase of combustion were significantly higher than all other Western United States

fueltypes measured (Hardy and Teesdale 1991)

24
In some areas of the Western United States, historical fire suppression has allowed

the encroachment of western juniper (Juniperus occidentalis Hook ) into rangeland

Prescribed fire is effective at controlling juniper felled to provide ladder fuels Smoke

exposure during juniper burns is most likely during holding operations

Stand replacement burning—Burning to improve large-game habitat and restore fireadapted ecosystems in the Rocky Mountains is often accomplished in lodgepole pine

(Pmus contorta Dougl ex Laws) and spruce (Picea sp ) at high elevations and in oak

brush stands after spring greening has occurred These fires are typically prescribed

as stand-replacement burns to remove decadent, overstocked forests (Oberheu

1995) Most units are ignited by hand with drip torches The high fuel moisture of

green vegetation would be expected to result in a high proportion of CO and other

products of incomplete combustion The prescription often targets an active crown

fire behavior, and natural barriers are relied on to contain the fire as opposed to

firefighters, who would be ineffective against such a fire Also, mop up usually is

not done because of the remote locations burned These two factors combine to

limit smoke exposure among the fire lighters to occasional wind-driven events

(Chonka 1995)

Taiga—Prescribed fire in Alaska is done chiefly to improve wildlife habitat on public

lands throughout the State and, to a lesser extent, for wildfire hazard reduction, especially near inhabited areas where fire suppression historically has occurred (Van

Der Linden 1995) In absolute terms, the annual acreage burned in Alaska is small

Prescribed fires often are large landscape-scale, stand-replacement burns, which

allows the use of natural barriers and minimizes the need for firehne holding Fuels

include mostly black spruce (P manana (Mill) B S P ) and feathermoss associations

(Viereck and others 1992) of the taiga Smoldering combustion is strong in the

feathermoss layer, but mop up rarely occurs When adjacent resources require protection from the prescribed fire, firefighters engaged in holding firehnes and direct

attack can be expected to encounter significant smoke Such situations can occur

when prescribed fire is applied to create a fire barrier at an urban interface (Ricker

1995)

Wetlands—In the Southeast United States, prescribed burning is sometimes required

in marshy areas called "pocosin," which have a very deep organic layer The fuels are

analogous to peat bogs in the Great Lakes region When sufficiently dry, the organic

layer can support vigorous smoldering combustion, often burning deep below the

ground surface The smoke is very acrid and causes severe irritation of the eyes and

upper respiratory system (Kubiak 1995)

Wildfire Suppression Wildfires and fire suppression tactics differ across the United States owing to regional

and local differences in fuel type and arrangement, weather, suppression resources,

and agency goals Topographical relief and the resources at risk in a particular fire

contribute to decisions about the appropriate management strategy to suppress the

fire Weather, as it affects actual and predicted fire behavior, is perhaps the most

important and unstable variable controlling suppression options

Wildfire suppression tactics begin with an initial assessment of the situation, followed

by attack of the fire by the first resources at the scene perhaps supplemented by

late-arriving suppression forces The strategy may be one of either direct or indirect

attack, but the goals are to contain and extinguish the fire Containment is achieved

by natural or artificial barriers to prevent further spread of the fire Roads, natural

25
barriers, firelines, and backfires may be used for containment Extinguishing the fire

is achieved by removing heat, oxygen, and fuel.

Wildfire Literature Smoke exposure at wildfires has been more widely studied than smoke exposure at

prescribed fires. The publications detailed below have examined smoke exposure

among wildland firefighters

Jackson and Tietz (1979)—The 1979 report by Jackson and Tietz broke important

new ground by examining the question of smoke exposure among wildland firefighters The study examined CO exposure at both wildfires and prescribed fires

Results are discussed here from sampling at 11 wildfires from 1974 to 1976. An

earlier publication summarized results from the first two wildfires in the project (Tietz

1975) Methods and their limitations were discussed above in "Prescribed Fire "

In Tietz (1975), both smokers and nonsmokers were included in the data Observations at the Outlaw Fire in Idaho concluded that 86 percent of 30 firefighters exceeded

5 percent COHb at either the beginning or end, or both, of their shift, and that a

nightly atmospheric inversion may have been the cause of these results The Outlaw

Fire burned in cedar (Thuja sp ), larch (Lanx sp ), and fir (Abies sp.) fuels At the

Deadline Fire in Idaho, 21 percent of 293 firefighters exceeded 5 percent COHb.

The Deadline Fire burned in ponderosa pine, lodgepole pine, and cottonwood

(Populus sp.).

The Jackson and Tietz (1979) data from wildfires consisted of 1,396 pairs of observations of COHb at 11 wildfires. Of these, 132 (9.4 percent) of the postworkshift levels

were above 5 percent COHb, generally accepted as the lower limit for acute health

effects The percentage of firefighters exceeding this 5-percent COHb limit ranged

between 0 and 100 percent of those measured, depending on the wildfire. Firefighters

were implementing a direct attack fire plan at all wildfires The researchers observed

that initial attack posed the greatest CO hazard among the firefighters, with 87 percent of the firefighters assigned to initial attack exceeding the 5-percent COHb standard (one of these initial attack incidents was a prescribed burn with a slopover). The

initial attack crews had the highest COHb levels, ranging up to 8 percent.

Some narrative descriptions of the monitoring are provided for the 1976 field season.

Although observation of work activities was not rigorous in this project, some clues as

to the cause of high COHb levels may be obtained from the narratives At the Ingalls

Creek Fire in Washington, 7.6 percent of 300 observations over 4 days exceeded

5 percent COHb at the end of a shift No description of work activities was made

Fuels were subalpine conifers with grasses, a thin litter layer, and little duff Winds

were between 5 and 10 m p h

At the Spring Canyon Fire in Utah, 1 of 34 firefighters (3 percent) exceeded 5 percent

COHb The fire was under control by the time sampling commenced, therefore mop

up may have been the only major work activity still occurring. Fuels consisted of sagebrush and grass. Winds ranged between 10 and 15 m.p.h., a possible cause of the

single high smoke exposure.

The Roy Lake Fire in Minnesota involved mixed jack pine (Pmus banksiana Lamb ),

spruce (Picea sp.), and aspen (Populus tremuloides Michx.) with heavy litter and a

thick duff layer. Winds averaged 10 m.p.h with gusts to 22 m p h Of the 380 COHb

observations, 55 (14.5 percent) exceeded 5 percent COHb, with almost all occurring

before the fire was controlled The authors note that high CO exposure was directly

associated with proximity to the head of the fire

26
At the Jeannot Creek Fire, Idaho, in mixed conifers and grasses, winds ranged

between 10 and 20 m p h and the fire was contained before monitoring began Even

so, 10 of 202 firefighters exceeded 5 percent COHb evidently owing to smoke from

heavy fuels smoldering within the fire perimeter

At the Walsh Ditch Fire in Michigan, 269 observations were made The TWA exposure limit was exceeded in 10 (3 7 percent) of those observations Winds ranged

between 5 and 10 m p h The fire, burning in peat grass, and hardwoods, apparently

was approaching containment by the time sampling began

The Dunham Creek Fire in Montana resulted in 100 percent of 14 smokejumpers exceeding the 5-percent COHb standard after their initial attack on the fire Winds ranged

between 10 and 15 m p h , and the fire was burning in larch and spruce logging slash

Line digging and mop up were the work tasks in "medium to heavy smoke "

The D Road Fire, Montana, was in lodgepole pine and spruce logging slash, with

gusty winds ranging between 15 and 30 m p h Of 69 measurements, 12 (17 3 percent) exceeded 5 percent COHb These were all associated with the initial attack

crew on the first day of the fire

Clearly, firefighters in the initial attack experienced CO exposures high enough to

produce elevated COHb levels Of the fires in 1976 for which narratives are available,

a trend seems to associate higher smoke exposures with higher windspeeds when

medium to heavy fuels are present Smoke exposure also seems to decline as a fire

progresses from initial attack to mop up More conclusions might be possible with a

thorough review of the raw project data

Griggs and others (1983)—This report evaluates CO exposure during suppression

of a brush and peat ground fire in North Carolina (Griggs and others 1983) Data were

collected by the University of North Carolina School of Medicine and the U S Environmental Protection Agency, Environmental Monitoring Systems Laboratory, during

1 day of firefighting The sampling occurred after the fire had been contained, 2 days

after high smoke exposures had resulted in hospitalization of several firefighters for

smoke inhalation Blood COHb was determined directly by gas chromatography of

blood samples from firefighters who had been either upwind or downwind of the fire

Sampling occurred in late morning and was repeated 2 hours later Some area

samples of ambient CO or grab samples of breathing zone CO also were obtained

No quality assurance data are reported Ambient winds were around 6 m p h Smoke

exposure on the downwind side of the fire was described as "moderately heavy"

Firefighters were operating pumps and other equipment to drown the ground fire

Their exertion levels were described as no more than moderate

Ambient CO levels averaged 75 ppm on the downwind side of the fire, with a peak

level of 200 ppm Upwind concentrations of CO were less than 10 ppm The authors

report that CO concentrations at another peat ground fire reached 500 ppm Latemorning blood COHb levels ranged between 6 and 13 percent in smokers downwind

of the fire and between 4 and 5 percent in nonsmokers Repeat measurements from

the same individuals 2 hours later showed that smokers' COHb declined to between

5 and 6 percent and nonsmokers' COHb increased during the same period to between 6 and 7 percent Thus both smokers and nonsmokers achieved an equilibrium

COHb level consistent with the average ambient CO concentration, according to the

authors Upwind nonsmokers had COHb levels in the 1- to 5-percent range One

smoker operating a tractor in dense smoke on the upwind side had a COHb level of

27
9 percent Because the sampling occurred late in the fire when smoke intensities were

lower, the authors concluded that intensive work on the firehne 2 days earlier could

have resulted in higher COHb levels when the firefighters had required hospitahzation

Sutton and others (1988)—This draft report discusses an emergency response to

evaluate smoke exposure among firefighters at the Klamath National Forest, northern

California, during the 1987 Happy Camp fire complex (Sutton and others 1988) Some

of the information in this document is summarized in a later article covering several

years of work (Materna and others 1992a). Ambient CO was measured at four locations in the area by using active-type colonmetnc detector tubes. Seven fire crews

were administered health evaluation questionnaires and tested for blood COHb by

measurement of CO in end-exhaled breath. The COHb was calculated from exhaled

air by using the Haldane equation (Stewart and others 1976) The CO analyzer used

was calibrated only after the sampling, which may have affected the accuracy of the

results Quality assurance data were not reported Total particulate matter exposure

samples were collected from five firefighters with NIOSH method 0500 One 20-

person crew was sampled during night shift line construction for benzene exposure

by using passive sorbent badges. Firefighters were nonrandomly selected for monitoring based on their proximity to the fire, recent assignment to the firehne, and accessibility for sampling.

Results of ambient CO sampling ranged between 4 and 10 ppm in fire camp and at a

remote drop point. The authors note that ambient CO monitoring by Siskiyou County

Air Pollution Control District 2 days earlier had measured a maximum hourly average

of 54 ppm CO in the fire camp, although the levels had decreased to about 11 to 12

ppm on the days of the study as a result of decreased atmospheric stability. Ambient

CO sampling on the firehne ranged from 22 ppm on the fireline and 25 ppm near a

chainsaw, up to 200 ppm near a water pump.

Questionnaires given to the firefighters showed a high prevalence of headaches

(59 percent), cough (66 percent), shortness of breath (38 percent), hghtheadedness

(32 percent), and wheezing (31 percent), among other adverse symptoms. Blood

COHb was not reported in the draft report, but exhaled CO concentrations were

reported to range between 9.1 and 53.2 ppm, with mean values between 13.0 and

25 7 ppm for subgroups of fire personnel. Smokers had higher COHb levels than

nonsmokers. Results of benzene exposure sampling from a crew working line

construction on the night shift were mostly below detection limits (0.07 ppm), with

one at 0.08 ppm and one unusually high sample at 0.5 ppm. No explanation was

given for the high sample result

Dust sampling was conducted for 1 day, with sample durations between 4 and 180

minutes. One 180-minute sample from a security checkpoint at Happy Camp found a

TPM exposure of 1.8 mg/m3. Ambient monitoring by the Siskiyou County Air Pollution

Control District 3 days before had found a maximum 24-hour average of 4.6 mg/m3 in

Happy Camp, and 9 days in which the concentration ranged between 1 0 and 3 0

mg/m3 The U.S. Environmental Protection Agency's national ambient air quality

24-hour standard for total suspended particulates (TSP) was 0.26 mg/m3 (TSP is essentially equivalent to TPM). On the days of this study, the 24-hour TSP levels were

0 455 and 0.578 mg/m3. A 17-minute sample and a 180-minute sample from a remote

drop point had similar results of 3.6 and 4.4 mg/m3, respectively. Short-term TPM

sampling of two firefighters from a type I crew gave results of 7.3 and 17 5 mg/m3 on

the fire line

28
The authors concluded that firefighters may have been exposed to sufficient ambient

CO to exceed 5 percent COHb levels, with associated performance impacts that

could be hazardous to the firefighters and their coworkers Engine and pump operators were considered likely to have high levels of COHb Ambient CO exposure had

declined from levels measured just a few days before thus the COHb levels might

have been even higher earlier in the fire Hours of physical exertion and cigarette

smoking were shown to be independently associated with exhaled CO, and smoking

firefighters were likely to have greater COHb concentrations than were nonsmokers

The high prevalence of respiratory symptoms were associated with dust exposure,

which could exceed recommended standards Benzene exposure was minimal, based

on the limited sampling

Among their recommendations, the authors suggested further industrial hygiene monitoring of CO and particulate matter in various fire and weather combinations Crossshift pulmonary function testing also was recommended Disposable dust masks were

recommended to reduce dust exposure, as was in house industrial hygiene capability

and a medical surveillance program

Reinhardt (1989)—Included in this preliminary evaluation of smoke exposure among

firefighters at prescribed burns (described earlier in this review) were 2 days of smoke

exposure sampling at northern California wildfires, one during nighttime mop up in

oak and grass rangeland and the other during mop up in chamise chaparral and pine

(Reinhardt 1989) California Department of Forestry and Fire Protection (CDF) and

USDA Forest Service firefighters were nonrandomly selected to characterize the

range of smoke exposures Sample durations ranged between 15 and 200 minutes

Mean CO exposure was about 22 ppm in chaparral and about 17 ppm in the oak and

grass Mean HCHO exposure was about 0 1 ppm in chaparral and 0 02 ppm in the

oak and grass The nighttime sampling was under inversion conditions, and smoldering heavy fuels, duff, and litter were the primary smoke sources No conclusions

can be drawn from this limited sampling other than the potential for exposure to significant levels of CO and moderate levels of HCHO

Brotherhood and others (1990)—This study from the Australian National Institute

of Occupational Health and Safety assessed CO exposure among bushfire fighters

during experimental fires in dry eucalyptus (Eucalyptus sp ) forests in Australia

(Brotherhood and others 1990) Carboxyhemoglobin levels in 24 male firefighters (15

smokers and 9 nonsmokers) were studied from measurements of CO in end-exhaled

breath The method of Smith (1977) was used to relate these alveolar CO levels to

predicted COHb concentrations Quality assurance data were not reported Firefighters were observed as they participated in direct attack of experimental fires and

constructing firelines with hand tools and chamsaws Fifteen direct-attack exercises

were conducted with fires, the average duration of each was 86 minutes (range 37

to 187 minutes) Blood COHb also was determined from firefighters during 11 simulated direct attacks where no fire was present Two other work activities were evaluated on separate occasions backfiring, where firefighters held line and mopped up

for 7 5 hours, and bulldozer line construction, where the firefighters using wildland fire

engines held line and mopped up behind the bulldozer for about 2 hours In addition

to data from the experimental fires, blood COHb was assessed in 12 nonsmoking

scientific observers at the scene who followed the firefighters

29
The study found that smokers averaged 3.4 percent COHb before the experimental

fires, and nonsmokers averaged 0.7 percent COHb. During the direct attack experiments, COHb increased in both groups at about 0.68 percent COHb per hour in the

firefighters, and 0.32 percent per hour in the observers, who exerted less effort during

the experiments. COHb was measured in firefighters within 40 minutes of completion

of work and found to average 4.4 percent in the smokers and 2 percent in the nonsmoking firefighters. The maximum COHb observed in the direct attacks was 8 6 percent in the smokers and 4 7 percent in the nonsmokers.

During the backfiring operation, COHb increased by 1.4 percent in the first 1.25 hours

before lunch and another 1.5 percent in the 6.25 hours after lunch. Final COHb concentrations were 7 percent (maximum 8.4 percent) in the smokers and 3.2 percent

(maximum 5 6 percent) in the nonsmokers. During the bulldozer line construction,

COHb increased by 1.5 percent in both groups, with final levels of 5.4 percent in the

smokers and 3.2 percent in the nonsmokers. During nonfire exercises, the COHb of

all participants decreased.

The authors calculated the environmental CO exposure of the participants based on

the alveolar CO via the Cobum-Forster-Kane (CFK) equation (Coburn and others

1965). The mean CO exposure attributed to the fires during the direct attack exercises was estimated to be 13.5 ppm (range: 3 to 40 ppm). This was about equal to

the CO exposure attributed to cigarette use among the smokers (who thus nearly

doubled their CO exposure). During the backfiring operation, CO exposure averaged

26 ppm among the nonsmokers (maximum- 38 ppm) and CO exposure averaged 30

ppm (maximum: 50 ppm) during the bulldozer line construction. In the simulated direct

attacks without fire, environmental CO was estimated to be 3 ppm (range. 1 to 6 ppm)

for the nonsmokers.

Because the measurements were obtained over relatively short durations, the authors

estimated the COHb levels that would result after 8 hours of exposure by using the

CO levels estimated from the CFK equation and alveolar CO measurements (assuming a reduced work rate); results were COHb levels averaging 5 percent (maximum:

11 percent) in smokers and 3 percent (maximum: 7 percent) in nonsmokers. They

further estimated that COHb would exceed 5 percent in fewer than 7 percent of the

fires. They concluded that CO exposure among nonsmokers was generally low during

direct attack of Australian bushfires.

They compared their results with those of Jackson and Tietz (1979) and estimated

that the latter's use of the Rmgold equation (Ringold and others 1962) to relate

alveolar CO to COHb would result in a bias of +1 percent in estimated COHb. On

that basis, they stated that the percentage of exposures exceeding 4 percent COHb

(rather than 5 percent) would be comparable The authors conclude that COHb levels

below 10 percent would have negligible health or work capacity effects in healthy

adults, and most CO exposures among Australian firefighters therefore would not be

likely to cause adverse health effects.

30
Letts and others (1991)—This work was conducted by NIOSH on behalf of the National Park Service in 1990 to evaluate cross-seasonal changes in lung function and

respiratory health (Letts and others 1991) Six type I crews from the National Park

Service and the Forest Service stationed in southern California underwent preseason

and postseason pulmonary function tests and completed respiratory symptom questionnaires. Spirometric measurements of FVC, FEV1, and FEF25-75 were obtained

from each firefighter and the ratio of FEV1 to FVC was computed In all, 78 of 105 fire

fighters completed both the preseason and postseason testing. Fifteen weeks of fire

season elapsed between the two testing dates Some bias in the results is possible

because the firefighters unavailable for postseason testing were younger and less

experienced than those completing the testing, and the younger firefighters originally

had slightly greater baseline FVC and FEV1

Each crew foreman subjectively estimated the smoke intensity for each day of firefighting during the fire season, and a weighted index of smoke exposure was calculated for the season by multiplying the number of hours of firefighting by the smoke

intensity for each fire. The crews were then divided into three exposure categories

(low, medium, and high)

Health symptoms either declined or changed slightly across the fire season Among

the firefighters who developed respiratory symptoms by the end of the season, only

throat irritation was associated with smoke exposure (with little statistical significance)

Lung function changed slightly across the fire season averages were -0 5 percent for

FEV1, +0.2 percent in FVC, -2 3 percent for FEF25 75 and -0 5 percent in FEV1/FVC

These changes were not statistically significant, although the decline in FEF25 75 was

nearly so (p=0.08). Changes in lung function of asthmatics were no different from the

rest of the firefighters When compared by exposure category, all lung function indices

decreased the most in the high-exposure category, but only the decrease in FEF25-75

approached dose-response linearity (p=0.08), with changes of +0 5 percent, -1.9 percent, and -4 7 percent for the low-, medium- and high-exposure groups, respectively

The authors note that declines in FEF25-75 indicate constriction of peripheral airways

(small bronchi and bronchioles), where chronic airflow-constricting diseases originate

The firefighters considered the 1990 fire season to be unrepresentative, with fewer

hours on the firehne than usual. Thus the results could underestimate respiratory

changes associated with a more active fire season Also, the effects of firefighting on

previously unexposed workers could not be detected because these were experienced firefighters with many years of service (and possibly, respiratory capacity loss)

prior to the "baseline" test. Finally, the exposure category classification may be inaccurate because smoke concentrations differ widely in a given day at a fire, thus the

total hours per day should not be equally weighted by a single recollection of smoke

intensity. The authors concluded that changes in lung function may have occurred

across the fire season and that studies should be conducted to examine cumulative effects of firefighting A comprehensive respiratory surveillance program for firefighters was suggested, as was respiratory protection and exposure monitoring

31
Rothman and others (1991)—This study from the Johns Hopkins School of Hygiene

and Public Health evaluated cross-seasonal changes in pulmonary function and respiratory symptoms in CDF firefighters from northern California during the 1988 wildfire

season (Rothman and others 1991) The study was restricted to nonsmoking (for

6 months) firefighters Spirometric measurements of FEV1 and FVC and a work

practices-respiratory symptoms questionnaire were obtained from each firefighter

Baseline data were collected in July after the fire season had begun, postseason data

were collected 8 weeks later Prebaseline firefighting activities were reconstructed

from California Department of Forestry fire station logs Daily firefighting hours during

the study period were self-reported by the firefighters

Fifty-two of 69 firefighters (75 percent) completed both the preseason and postseason

questionnaires and 50 also completed the spirometric measurements The 17 firefighters unavailable for postseason testing were not absent because of pulmonary

complaints, other demographic information on this group was not significantly different

from those completing the study On average, 18 hours of firefighting had occurred in

the month before the baseline measurements, and firefighters worked an average of

98 hours at fires during the last month of the study

The authors found a significant increase in eye and nose irritation, cough, phlegm and

wheezing across the study period Spearman rank-order correlations were observed

between health symptoms and hours of firefighting late in the study Eye irritation

(p=0 001) and wheezing (p=0 07) were associated with firefighting activity during the

last 2 weeks of the study, and nose irritation (p=0 08) was associated with firefighting

activity in the last week of the study

Baseline spirometry was not associated with the number of previous firefighting seasons Across the study period, changes in FEV1, FVC, and FEV1/FVC were -1 2 and

0 3 percent, and -0 006, respectively FEV1 was associated with hours of firefighting

in the final week (p=0 006), this association with weekly hours of firefighting weakened with elapsed time before the postseason testing Similar trends were found in

the association between FVC and hours of firefighting in the study period, with hours

in the final week showing the strongest association with decline in FVC (p=0 02)

Changes in FEV1/FVC were not associated with the firefighting hours Because of the

variability in hours of firefighting in the last week (range 0 to 125 hours), the firefighters were divided into groups of none, low, and high firefighting activity The FEV1

and FVC declines showed significant correlation with the exposure category for the

final week

The authors concluded that small but significant declines were seen in FEV1 and

FVC, and that these were associated with firefighting activity in the final week of the

study They questioned the accuracy of the self-reported hours of firefighting as an

indicator of smoke exposure, because of the lack of objectivity and the widely different

levels of smoke exposure at wildfires The possible reversibility of acute respiratory

impacts was raised, because the study design was not intended to demonstrate

whether the pulmonary function declines were the result of exposure over the season

or over the last 2 weeks of the study They recommended comprehensive assessment of the health and safety hazards of wildland firefighting They suggested that

respiratory irritant protection be made available and crew rotation be more frequent

32
Reh and Deitchman (1992)—This NIOSH project assessed smoke exposure among

firefighters at Yellowstone National Park in August 1988 on behalf of the National

Park Service (Reh and Deitchman 1992). The study sampled smoke exposure among

22 firefighters on 3 separate days at the Shoshone, Clover Mist, and North Fork fires

Firefighters at the Shoshone fire were engaged in mop up during their workshift. At

the other two fires, fireline construction was the major task

Breathing zone samples of CO, CO2, sulfur dioxide (SO2), and nitrogen dioxide (NO2)

were collected from the firefighters. Area samples for those compounds and TPM,

volatile organic compounds, aldehydes, and polycyclic aromatic hydrocarbons (PAHs)

also were collected. The CO, CO2, SO2 and NO2 sampling was accomplished with

colonmetric passive diffusion tubes. Total particulate matter was sampled with NIOSH

method 0500. Volatile organic compounds were sampled with NIOSH methods 1003,

1500, and 1503. Aldehydes were monitored with NIOSH method 2539 Sampling for

PAHs was done with NIOSH method 5515 No quality assurance data were reported

Volunteers were solicited from the crews being monitored for smoke exposure for a

medical evaluation of exposure to CO and irritants The medical evaluation consisted

of a preshift and postshift symptom questionnaire and measurements of heart rate,

breathing rate, blood oxygen saturation, and blood COHb. Blood oxygen was measured on-site with a transcutaneous blood oximeter, and COHb was measured by

blood sample and off-site COHb analysis.

All dosimeter data for the Clover Mist fire were invalidated because the crew worked

a 24-hour shift that exceeded the time limits of the dosimeter tubes. Only dosimeter

data for CO were available for the Shoshone fire. Personal monitoring results for the

North Fork fire showed that CO ranged between 3.6 and 7.8 ppm (TWA) during mop

up, and between 1.9 and 3.9 ppm during 1 day of fireline construction Carbon dioxide

TWAs were all 1,000 ppm, and SO2 measurements ranged between nondetectable

and 1.2 ppm. Measurements of NO2 were all below the detection limit of 0.2 ppm.

The authors characterized the atmospheric conditions as "light smoke" for the period

under study.

Area sampling lasted between 3.5 and 11 hours and found CO levels of 1.6 to

6.2 ppm in fire camps, up to 23.3 ppm on the fireline at the Shoshone fire, 4.6 ppm

at the Clover Mist fire, and 11.5 ppm at the North Fork fire. Area samples of CO2

ranged between 700 and 750 ppm on the fireline, and up to 1000 ppm in fire camps.

Samples of SO2 showed 1.0 ppm in fire camp, and up to 1 9 ppm on the fireline at

the Clover Mist fire. Area results for NO2 were below detection limits. Most area

sampling results for TPM ranged between 0.1 and 1 2 mg/m3and two samples were

higher: a 5-hour sample at the Clover Mist fire was 15 9 mg/m3, and a 4-hour sample

at the North Fork fire was 47.6 mg/m3. The fire camp samples were all between 0 1

and 0.6 mg/m3. Four aldehyde samples detected only HCHO at average levels

between 0.02 and 0.03 ppm. The results of area sampling for volatile organic compounds were all low, below 0.03 ppm for benzene ana 0 05 ppm for furfural. Area

samples of PAHs over the same periods detected only gaseous-phase naphthalene

(maximum of 3.53 mg/m3, fluorene (maximum of 1 04 mg/m3), and acenaphthene

(maximum of 1.53 mg/m3).

33
A slight increase in eye, nose, and throat irritation was noted from the preshift and

postshift symptom surveys A statistically significant increase (p=0 04) was found in

the number of firefighters reporting decreased alertness Blood oxygen saturation

showed no significant changes between measurements The highest COHb level

(4 7 percent) was in a smoker prior to the workshift Levels of COHb decreased an

insignificant amount in the crew performing mop up at the Shoshone fire, decreased

significantly (p=0 005) in the crew performing line construction at the North Fork fire,

and increased significantly (p=0 001) for the crew constructing a fireline at the Clover

Mist fire The crew at the Clover Mist fire worked a 24-hour shift and had their postshift COHb measurements collected in the morning hours

The authors concluded that the exposures on the days sampled were mostly below

applicable exposure limits and did not pose a hazard to the workers Most of the area

samples also were below the evaluation criteria, although the authors noted that the

fire camp levels of CO were similar to those measured at the fireline, and thus the fire

camps could not be considered adequate CO-free zones The dosimeter tube results

for SO2 mostly exceeded 50 percent of the exposure limit criteria, an observation

attributed to geothermally derived sulfur in local soils Subsequent discussions with

NIOSH raised doubts about the accuracy of these and later SO2 measurements by

NIOSH because the dosimeter technology may be positively biased by other constituents in smoke (Kelly 1994) Of the area samples, two TPM samples exceeded occupational exposure limits

The authors mentioned that the "nuisance dust" classification was probably not appropriate for the TPM, because the TPM was likely to be composed of toxic chemicals

The authors proposed modified exposure limits for CO using the CFK equation to

account for the high altitude, heavy work rate, and long shift length that the firefighters

experienced They also proposed modified exposure limits for NO2, PAHs, aldehydes,

and volatile organic compounds using the OSHA time-adjustment model to adjust exposure limits The authors concluded that the exposures measured could not be generalized to all firefighters because smoke exposure could be higher in different circumstances They recommended further study in smokier conditions and evaluation of the

smoke exposure potential of different work activities, such as direct attack, holding

line, and burnout operations Chemical characterization of the TPM is recommended

for future industrial hygiene sampling

They concluded that the observed medical symptoms could be associated with smoke

exposure and that the lack of significant increases could be due to previous fireline

exposures among the crews before the baseline measurements Further, they men

tioned that two of the crews had a 1- to 2-hour hike through low-exposure areas

before the postshift measurements, which could result in an underestimate of COHb

levels because of CO elimination from the body

Administrative controls were recommended to reduce workshift lengths and the number of consecutive days on the fireline and to site base camps in smoke-free areas

Bandannas were not recommended, but single-use dust and mist filter respirators with

exhalation valves were recommended for interim respiratory protection, in conjunction

with a comprehensive respiratory protection program in accordance with OSHA

requirements

34
Harrison and others (1992)—This project report summarizes work in 1989 by the

California Department of Health Services on behalf of CDF and the Forest Service

(Harrison and others 1992) The study obtained cross seasonal pulmonary function

and smoke exposure measurements among firefighters during 3 days of prescribed

fires and 2 workshifts at a wildfire in northern California The general protocols of the

smoke exposure monitoring are described in this review (see Materna and others

(1992a),' below) At the Layman fire (in the Plumas National Forest) smoke exposure

monitoring captured two 12-hour workshifts The first workshift involved CDF fire

fighters performing engine-supported mop up of smoldering areas at the fire during

the day shift Subsequently, exposure monitoring was done on a Forest Service

hotshot crew during mop up in inversion conditions on the night shift

Because some of the exposure monitoring results are not differentiated by wildfire or

prescribed fire the general conclusions discussed in the Prescribed Fire section of

this review may apply to the wildfire monitoring results as well Of the results spe

cific to the Layman fire, between-day comparisons were made by assessing differences between mop up during the day and during the evening inversion Mean HCHO

exposure was not found to differ significantly (p=0 1) among shifts but CO and respirable particulate exposures were significantly different The mean CO concentration

was 9 3 ppm during the day shift and 17 1 ppm during the evening shift The mean

PM3 5 concentration was 0 62 mg/m3 during the day shift and 1 83 mg/m3 during the

evening shift In view of correlations observed among CO PM3 5 and HCHO at

prescribed fires (Reinhardt and others 1994) and remote wildfires (Reinhardt and

others 1995b), the nonsignificant difference of the HCHO levels between the two

shifts may be a result of low-concentration samples and variation in analytical values

caused by the high detection limit of the NIOSH method used

Sixty-three firefighters from CDF and the Forest Service were tested before and after

the 1989 fire season for pulmonary function (FVC FEV1 and FEF25 75) as well as

methacholine challenge testing to determine their nonspecific airway responsiveness

(how much their airways constricted in response to increasing doses of methachohne)

This protocol was intended to assess susceptibility of individuals to adverse pulmonary effects from exposure to respiratory irritants The firefighters had exposure to

smoke at many wildfires during the fire season (averaging 58 days of exposure)

Only results for Forest Service hotshot crews were reported in Harrison and others

(1992) These data also are published in a journal article (Liu and others 1992) The

preseason and postseason pulmonary function testing found small but significant declines in FVC, FEV1, and FEF25 75 The postseason testing was within a week of the

last fire The methachohne challenge testing showed a significant association between

the log of the dose-response slope (how responsive the airways were to the methachohne) and an individual's history of allergies Further a history of asthma was associated with airway responsiveness, but the association was not statistically significant All firefighters had a significant increase in the mean dose-response slope

across the fire season their airways constricted more readily when exposed to

methachohne at the end of the fire season than at the beginning Individuals with

adverse health symptoms in the lower respiratory tract had a significantly greater

dose-response slope increase than the other firefighters as did those with a history

of asthma (although their difference was not significantly greater than the other

firefighters)

35
Materna and others (1992b)—This summary publication describes exposure monitoring by the California Department of Health Services from 1987 to 1989 (Materna

and others 1992b) Most details of the monitoring are discussed in the Wildfire

Supression section of this review and in the previously reviewed reports by Sutton

and others (1988) and Harrison and others (1992) Information from Materna and

others (1992b) not already mentioned include the results from monitoring for PAHs in

TPM These PAH results were obtained with NIOSH method 5506 at a wildfire in the

Lassen National Forest, northern California, in 1988

Twenty samples were obtained in the 1988 sampling, the mean sample duration was

345 minutes Twelve specific PAHs were identified in the samples, all at low levels

(<1 mg/m3) The sum of the PAHs was far below both the OSHA PEL of 200 mg/m3

and the ACGIH TLV of 50 mg/m3 The authors concluded that PAHs, although

carcinogenic were found only at very low levels in smoke samples

Among their general findings over the 3 years of study was the observation that exposure data were inadequate to evaluate the hazards of firefighting, thus they recommended that more data should be collected, especially for potential carcinogens and

crystalline silica Short-term sampling was recommended to assess acute smoke exposures They recommended medical surveillance for the workers to detect adverse

health effects They suggested that the OSHA PELs might not be sufficient to protect

workers' health, because of the extended workshifts and fire camp exposures, arduous work and high altitudes Also, the inert particulate standards were considered

inadequate to protect against the irritant and carcinogenic substances adsorbed on

smoke particulate Interim exposure management recommendations included frequent

crew rotations, shift limitations, and development of respiratory protection specifically

for wildland firefighters Feasibility studies were suggested for interim respiratory protection Training firefighters in the health hazards of smoke also was recommended

Kelly (1992a)—Smoke exposure data were collected on 3 days in July 1991 at the

Thompson Creek fire in the Gallatin National Forest by NIOSH on behalf of the National Park Service (Kelly 1992a) Personal exposure sampling was conducted among

two type I hotshot crews for CO, SO2, PM3 5, crystalline silica, and aldehydes Passive colorimetnc diffusion tubes were used for CO and SO2 Aldehydes were measured with NIOSH method 2539, and PM3 5 was measured with NIOSH method 0600,

followed by crystalline silica analysis with NIOSH method 7500 Half of all PM3 5

samples collected were analyzed for crystalline silica In addition, two area samples

were collected in fire camp on July 19 to evaluate off-shift exposures to PM3 5 and

crystalline silica during a visible inversion Quality assurance data were not reported

Twenty firefighters were monitored each day by using nearly full-workshift sample

periods

On the first day, firefighters were engaged in structure protection away from the fire,

smoke exposure was very low Almost half an inch of rain fell during the evening, thus

reducing the fire danger On the second and third days, the firefighters constructed

fireline and did some direct attack of spot fires Carbon monoxide exposure averaged

1 6, 6 9, and 6 2 ppm over the 3 days (range up to 17 ppm) Sulfur dioxide exposure

ranged between 0 6 and 3 0 ppm Aldehyde concentrations were low, ranging from

nondetectable up to 0 08 ppm HCHO, 0 06 ppm acetaldehyde, and 0 01 ppm furfural

Trace amounts of acrolein were observed Respirable particulate exposure averaged

0 37 mg/m and the highest PM3 5 exposure was 4 3 mg/m3 Two PM3 5 samples

36
had detectable amounts of crystalline silica One was low concentration but the other

had a quartz content of 0 35 mg/m3 Fire camp sampling found the PM3 5 and crystalline silica concentration to be low, and only trace amounts of aldehydes were

detected

The authors concluded that exposure to CO and aldehydes was low but that one

firefighter was overexposed to crystalline silica and several exceeded exposure limits

for SO2 The direct attack monitored in this project was neither prolonged nor particularly smoky The authors recommended that smoky events be measured only through

the establishment of a long-term routine monitoring program which is best accomplished by the agencies employing the firefighters

Materna and others (1992a)—This study, from the California Department of Health

Services, examined the feasibility of three different methods of assessing CO exposure among a type I handcrew of firefighters at the Finley Lake fire in northern

California during 1990 (Materna and others 1992a) Colonmetnc passive diffusion

tubes, electrochemical sensor dataloggers, and exhaled alveolar air testing were

evaluated In addition, CO exposures by work activity were to be compared through

self-reporting of work activity by the firefighters in pocket logbooks Finally a questionnaire was used to determine firefighter attitudes and knowledge about adverse health

effects of CO exposure Alveolar monitoring was related to COHb concentration

through the equation used by Brotherhood and others (1990) Postshift COHb mea

surements were made within an hour of departing the fireline No quality assurance

data were reported

Three evening workshifts were monitored in August 1990 Twenty-five firefighters from

one crew cooperated in the study Monitoring excluded travel time to limit sampling

data to fireline exposure only Based on logbook entries work activities included line

construction, back firing, and line holding on the first two evenings Mop up was the

primary activity during the third workshift

Exposure monitoring with diffusion tubes found a mean CO exposure of 8 2 ppm

(range 2 to 16 ppm) Electrochemical dataloggers had similar results, with a mean of

7 8 ppm Two of the 12 firefighters wearing the dataloggers had peak CO exposures

of 212 and 339 ppm These exposures were associated with mop up activities

Fifteen-minute peak exposure samples for CO were all 50 ppm or less, with the exception of 150 ppm for one firefighter The CO levels measured by the diffusion tubes

and dataloggers showed moderate agreement, with an r2 of 0 56 over all shifts, and

0 87 for just the first two shifts The diffusion tube readings were consistently higher

than the datalogger results for the third shift

Measurements of CO in alveolar air demonstrated small but statistically significant

increases in COHb across the workshifts The preshift COHb levels were high for a

nonsmoking group, averaging 1 7 percent COHb One firefighter's COHb level increased to 3 6 percent across the workshift, which is at the limit of the Biological Exposure Index recently adopted by ACGIH The authors noted that this firefighter's

TWA exposure was measured at 16 ppm, well below the 25 ppm TLV Two other

firefighters had postshift alveolar air measurements coiresponding to more than

3 percent COHb The diffusion tube results showed only fair agreement with the

cross-shift change in alveolar CO, the r2 for the 51 pairs of measurements was 0 37

37
Only 8 of 25 activity logbooks were returned to the researchers, thus the planned

comparison of exposure versus activity could not be done The firefighters' responses

to the CO exposure questionnaire demonstrated a high level of interest in the hazards

of CO exposure and a desire to monitor their own exposure Most of the firefighters

correctly identified one or more symptoms of CO exposure, but many incorrectly associated additional health effects to CO poisoning A high percentage of the firefighters reported that they experienced adverse health effects while working at fires

The firefighters associated direct attack, heavy smoke conditions, and mop up tasks

with high CO exposure

The authors concluded that the CO exposures measured were low in comparison to

other monitoring The prevalence of peak CO exposures above 200 ppm (17 percent

of 12 samples) caused the authors to recommend further evaluation of short-term CO

exposures The three methods of CO exposure monitoring had advantages and disadvantages The diffusion tubes were simple and inexpensive, moderately accurate,

and useful for acquiring large amounts of data A significant drawback was the lack

of response to peak exposures or warning to users about high CO hazard situations

The electrochemical dataloggers were very useful for detailed data collection and

associating CO exposure with work activities and situations The dataloggers required

more skills to calibrate and retrieve data but were simple to use in the field The

dataloggers drifted in their measurement of zero CO The high initial cost and periodic

maintenance requirements were disadvantages of the dataloggers The technique of

analyzing the last portion of an exhaled breath was relatively easy to perform but had

high initial costs and periodic maintenance requirements The advantage of biological

monitoring was cited, because the method assesses the delivered dose regardless of

individual differences in CO uptake and elimination Assessing CO exposure by

preshift and postshift COHb measurements may miss detecting overexposure to CO

early in the workshift, because COHb from such an exposure may be eliminated by

the time the postshift measurement is made

The authors recommended that postshift alveolar air measurements be taken at the

fireline rather than in fire camp The choice of CO monitoring method was left open

the answer depends on the purpose of sampling, budget, size of project, accuracy

needed, and field personnel capabilities Additional exposure monitoring was recom

mended and should be aimed at associating CO exposure levels with specific work

activities and conditions Dataloggers were suggested for this Direct observation,

rather than self-reported logbooks, was recommended for obtaining work activity data

Development of practical smoke exposure controls is recommended for high exposure

situations Training is recommended for all wildland firefighters, to communicate the

hazards and symptoms of overexposure to smoke and ways to reduce health risks

Equipment for CO monitoring is recommended for large fire camps to assess camp

exposure and screen suspected cases of CO poisoning Passive diffusion tubes are

recommended for widespread data collection Medical surveillance programs also are

recommended for wildland firefighters

38
Kelly (1992b)—This study by NIOSH took place at the Gauley Mountain fire in West

Virginia during November 1991 on behalf of the National Park Service (Kelly 1992b)

Two days of smoke exposure monitoring were accomplished by using the same

methods described above (Kelly 1992a), with the addition of benzene soluble PAHs

measured with NIOSH methods 5023 and 5515, and volatile organic compounds

(benzene, toluene, xylenes, and trimethylbenzene) measured with NIOSH methods

1003, 1500, and 1503 No quality assurance data are reported Full-workshift sampling was employed and was supplemented by ambient air measurements at a

visitors' center

Twenty firefighters from a type I hotshot crew were monitored for 2 days On the first

day, firefighters conducted a back-firing operation and held line on a road below the

backfire—smoke exposure was described as very low On the second day indirect

attack was done, followed by the setting of back fires from another dirt road Smoke

exposure was low for most of the shift and moderate for less than 1 hour during the

back-firing operation Average exposure to CO was 4 ppm (range up to 9 ppm)

Average exposure to SO2 was 2 ppm (range up to 9 ppm) Over half of the SO2

samples were above the NIOSH recommended exposure limit of 2 ppm Formaldehyde exposure ranged up to 0 1 ppm (average 0 07 ppm) The maximum furfural

exposure was 0 03 ppm Acetaldehyde and acrolein exposures were below 0 06 and

0 02 ppm, respectively Volatile organic compounds were not detected, in spite of a

9 parts per billion detection limit for benzene Exposure to PM3 5 averaged 0 49

mg/m3, with a high of 1 5 mg/m3 Crystalline silica was not detected Vapor-phase

PAHs were not detected, but particulate-phase PAHs were found at very low levels

Area samples showed very low concentrations for measurable pollutants

Recommendations included administrative controls that did not rely on subjective

estimates of smoke exposure to reduce SO2 exposure because the smoke intensity

did not relate to the measured SO2 levels Routine monitoring of smoke exposure was

recommended Longitudinal studies of the smoke exposure of individual firefighters

over the entire fire season were recommended Smoke exposure assessment at prescribed burns also was recommended, because the pianned nature of the burns facilitates logistical preparations and the data might prove comparable to wildfire results

Reh and others (1994)—This study by NIOSH was conducted in August 1990 at the

Arch Rock fire in Yosemite National Park of behalf of the National Park Service (Reh

and others 1994) Two days of smoke exposure data collection were accomplished

among three fire crews (two type I and one type II) Exposure data were supplemented by a medical survey among one of the type I crews and the type II crew The

breathing zone concentrations of CO, SO2, and NO2 were determined by colorimetric

passive diffusion tubes The diffusion tube sampling was supplemented by less extensive use of active sampling methods Sampling of PM3 5 exposure was done with

NIOSH method 0600 Volatile organic compounds were measured with NIOSH

methods 1003, 1500, and 1503 Aldehydes were monitored with NIOSH method 2539

Samples of gaseous and particulate PAHs were obtaired and then analyzed with

NIOSH method 5515 Air samples for hydrochloric hydrofluoric, sulfunc, hydrobromic,

nitric, and phosphoric acids were collected by using NIOSH method 7903 No quality

assurance data were reported

39
The medical survey consisted of preshift and postshift spirometnc measurements of

lung function (FEV1 FVC and FEF25 75) measurements of CO in alveolar air, and a

health symptom questionnaire The COHb levels were calculated from the alveolar air

measurements by using Ringold s method (Ringold and others 1962) Each firefighter

also was asked to estimate on a scale of 1 to 4, the smoke intensity during the

workshift

The two type I crews (the Pike and Plumas hotshots) conducted a burnout operation

on August 15 with the Pike crew lighting and holding the burnout in moderate smoke

and the Plumas crew holding a flank and mopping up in light smoke Sampling was

not done during the 2-hour hike to and from the fireline Among the Pike hotshots, CO

exposure averaged 18 3 ppm (range 6 1 to 24 2 ppm) and SO2 averaged 1 4 ppm

(range 1 1 to 2 4 ppm) Among the Plumas crew, CO averaged 3 9 ppm (range 1 2

to 9 4 ppm) and SO2 averaged 1 4 ppm (range 0 2 to 2 9 ppm) Sampling did not

detect NO2 exposure in either crew Sampling for PAHs detected low levels of gasphase acenaphthene (up to 1 0 μg/m3

), anthracene (up to 26 5 μg/m3 ), and naphthalene (up to 35 9 ug/m3

), and particuiate-bound acenaphthene (up to 1 7 μg/m3)

anthracene (up to 1 2 μg/m3), benzo(b)fluoranthene (up to 1 7 μg/m3), and fluoranthene (up to 9 3 μg/m3

) Aldehyde monitoring found low-level exposures to acetaldehyde (up to 0 04 ppm), acrolein (up to 0 01 ppm), HCHO (up to 0 07 ppm), and

furfural (up to 0 008 ppm) Sampling for acid gases found low levels of hydrochloric

acid (up to 0 04 mg/m3), sulfunc acid (up to 0 09 mg/m3), and hydrofluoric acid (up to

0 15 mg/m3) Respirable particulate matter exposure was higher among the Pike

crew (1 3 to 1 7 mg/m3) than the Plumas crew (0 6 to 1 1 mg/m3) Exposure to

volatile organic compounds was very low, with a maximum of 0 03 ppm for benzene

Twenty-one of 25 firefighters agreed to participate in the medical evaluation Preshift

COHb levels averaged 1 3 percent, postshift levels averaged 2 7 percent, with nonsmokers slightly higher than smokers The type I crew had a slightly higher postshift

COHb level (average 2 9 percent) in comparison with the type II crew (average 2 4

percent) No correlations were observed between the measured CO exposures and

the postshift COHb levels Lung function was found to decline across the workshift

averaging -0 7 percent in FVC, -1 2 percent in FEV1, -0 4 percent in FEF25 75 , and

-1 4 percent in the ratio, FEV1/FVC The declines in pulmonary function were larger

among the type I crewmembers and achieved statistical significance (p=0 05) the

declines among the type II crewmembers were not significant The cross-shift declines

were not correlated with self-reported smoke exposure Health symptoms increased

slightly across the workshift, with nose irritation showing the greatest increase of the

symptoms noted

Bandannas used by the firefighters were examined under an electron microscope

Measurements showed the pore size of the bandannas exceeded 100 micrometers

Thus they afford no protection against particulate matter having health significance,

let alone gas-phase pollutants

40
The authors concluded from their breathing-zone CO measurements that 30 percent

of the Pike hotshots exceeded an adjusted CO exposure limit of 21 ppm (based on

the CFK equation), and that the Plumas crew's exposure was within this limit Adjusted exposure limits were recommended for several components of smoke (using

the OSHA approach) They also found that the COHb evels increased across the

workshift, but that all were below 5 percent COHb The delay in postshift sample collection and the length of the shift relative to the half-life of CO were noted as possible

sources of bias in the results

The cross-shift declines in pulmonary function were small but significant For both the

type I and type II crews, FEVi losses were statistical significant Cross-shift losses

in FVC and FEVi/FVC were significant in one or the other of the two crews The

medical significance of these acute losses was not clear because none of the mean

changes exceeded 3 percent The authors report that other researchers do not consider declines in FEVi to be significant until they exceed 8 percent They considered

the small number of participants to be a factor limiting 01) association between selfreported smoke exposure and pulmonary function losses, and (2) the inability to demonstrate significant changes in adverse health symptoms The self-reported smoke

exposure also was considered to be a crude measure of exposure and possibly was

biased among those working a nighttime shift because of restricted visibility then

The authors recommended additional smoke exposure assessment to examine other

work activities and high-exposure situations Both TWA and peak exposures were

recommended for evaluation Collection of medical and epidemiological data was rec

ommended in concert with exposure assessments to establish dose-response relations The authors recommended banning bandannas to prevent any misconceptions

that they contribute to respiratory protection Disposable dust-mist respirators were

recommended, in conjunction with an approved OSHA respiratory protection program

Because the CO monitoring indicated exceedence of an adjusted CO exposure limit,

administrative controls were recommended to reduce CO exposure Among the

suggestions were reduced workshift duration, reducing the number of consecutive

days on the firehne, and locating fire camps in nonsmoky areas Routine CO and

SO2 monitoring by the agencies was recommended, and a respiratory health

surveillance program also was suggested

Betchley and others (1995)—The methods, study p pulation, and results of this

study (Betchley and others 1995) are described in detail above in the "Prescribed

Fire" section The authors found a small but statistically significant cross-season decline in the firefighters' mean pulmonary function indices This decline was reversed

and lung function returned to baseline levels by the start of the following season The

cross-season results and recommendations apply to wildfire suppression as well, because the firefighters had worked an average of six wildfires (range up to 24) during

the fire season

Reinhardt and others (1995a)—Smoke exposure among wildland firefighters in

Redding, California, was measured by the USDA Forest Service, Pacific Northwest

Research Station, and Radian Corporation on behalt ot the California Department of

Forestry and Fire Protection (Reinhardt and others 1995a) Firefighters from one fire

station were monitored during 11 days of initial attack responses in 1993 and 1994 to

provide a preliminary evaluation of smoke exposure during initial attack activities at

41
vegetation fires, determine whether smoke exposure exceeded occupational health

standards, and identify key factors that cause high smoke exposure levels The study

examined how smoke exposure differed among various work activities at wildfires and

tested correlations between smoke exposure and fire behavior determinants The

study also tested correlations among different pollutants in smoke to evaluate the

feasibility of estimating exposure to many pollutants from measurements of a single

pollutant

Sampling used only personal breathing zone measurements to assess smoke exposure Pollutants measured included acrolein and HCHO with EPA method TO-11,

benzene with NIOSH method 1501, CO and CO2 with Intersociety Committee Method

128, and PM3 5 with NIOSH method 0600 Electronic carbon monoxide dosimeters

(dataloggers) also were evaluated for accuracy and ease of use Peak and workshift

exposures were evaluated The authors considered the combined impact of respiratory irritants according to the OSHA model, calculating an equivalent respiratory irritant exposure index based on the exposure to acrolein, HCHO and PM3 5 (U S

Department of Labor 1994b)

Quality assurance data collected during the project indicated that the overall accuracy

of the exposure measurements (measured by percentage of recovery) was good for

CO and CO2 (100±8 and 3 percent, respectively), acceptable for benzene (100+23

percent), and relatively poor for some measurements of HCHO and acrolein (100±35

and 56 percent, respectively) Overall precision estimates (measured by relative

standard deviation of field replicates) ranged from 14 percent for CO2, to 24 to 33

percent for benzene, acrolein, CO, and respirable particulates, and up to 43 percent

for HCHO

The study calculated TWA exposures for 37 firefighters Smoke exposure was well

below occupational exposure limits at these vegetation fires, which burned mostly in

grass and oak savannah and some chaparral Individual fires were of short duration,

with a median time at the fire of about 4 hours On the other hand, the workshifts

(defined for exposure estimating purposes as the time from breakfast to the end of

active work during the day) averaged about 14 hours Table 5 shows the mean and

maximum TWA exposures averaged on the fireline and over the workshift

Brief occurrences of intense smoke exposure were common at the fires, but the

highest of these were within permissible short-term exposure limits set by occupational health agencies Mean and maximum peak exposures based on nominal

15-minute samples are shown in table 6

At difficult fires, overexposure to respiratory irritants and CO was considered possible,

based on interviews with experienced firefighters and the authors' observation of

missed sampling opportunities Smoke exposure during direct attack activities was

significantly higher than during mop up Table 7 shows the mean exposure by work

activity when firefighters were in or near smoke

Smoke exposure during all work activities except mop up increased linearly with

ambient (20-foot) windspeed between 5 and 15 m p h Electronic CO dosimeters

were considered practical devices for routine smoke exposure monitoring, although

a quality assurance program was indicated for their use to ensure valid data Insufficient data were available about the correlations among pollutants to eliminate the

need for comprehensive smoke exposure monitoring

42
Table 5—Time-weighted average exposures at small wildfires in northern

California

Pollutant

Acrolein (ppm)

Benzene (ppm)

Carbon dioxide (ppm)

Carbon monoxide (ppm)

Formaldehyde (ppm)

Respirable particulate (mg/m3)

Respiratory irritants (no units)

Duration13

Shift

Fire

Shift

Fire

Shift

Fire

Shift

Fire

Shift

Fire

Shift

Fire

Shift

Fire

Mean

0 002

0.010

0 003

0.017

394

508

1 9

7 0

0 009

0 039

0 24

1 07

0 08

0 43

Maximum

0.006

0.037

0.009

0.052

710

920

13

27

0.035

0.09

0.9

2.3

0.25

1.05

a

 Shift = entire workday; fire = portion of workday on fireline.

Table 6—Peak smoke exposures at small wildfires in northern

California

Pollutant

Acrolein (ppm)

Benzene (ppm)

Carbon dioxide (ppm)

Carbon monoxide (ppm)

Formaldehyde (ppm)

Respirable particulate (mg/m3)

Mean

0.018

0.035

642

14.3

0.117

2.08

Maximum

0.066

0.082

1265

42.2

0.339

6.88

43
n d = no data

A smoke exposure management program was recommended The recommendations

included establishing a baseline for smoke exposure at wildfires and prescribed fires

throughout California With such data, the true smoke exposure management needs

would be better defined, thereby allowing the development of efficient risk management strategies

Reinhardt and others (1995b)—Smoke exposure among wildland firefighters was

measured at five wildfires in the northwestern United States by the USDA Forest

Service Pacific Northwest Research Station, and Radian Corporation on behalf of the

National Wildfire Coordinating Group (Reinhardt and others 1995b) The same pollutants and methods outlined in Reinhardt and others (1995a) were used in this project

Objectives of the project were to develop a preliminary assessment of smoke exposure at wildfires identify key factors controlling smoke exposure among firefighters,

and evaluate correlations among pollutants to assess the feasibility of estimating exposure to many pollutants in smoke by measuring only one Electronic carbon monoxide dosimeters also were evaluated for accuracy and ease of use

Quality assurance data collected during the project indicated that the overall accuracy

of the exposure measurements (measured by percentage of recovery) was good for

CO and CO2 (100±8 and 3 percent, respectively), acceptable for benzene (100±23

percent), and relatively poor for some measurements of HCHO and acrolein (100+35

and 56 percent, respectively) Overall precision estimates (measured by relative

standard deviation of field replicates) ranged from 14 percent for CO2 to 24 to 33

percent for benzene, acrolein CO, and respirable particulate, to 43 percent for HCHO

Twelve days of data collection were accomplished at five wildfires between 1992 and

1994, average smoke exposures per workshift were calculated for 66 firefighters

Workshifts averaged 13 hours, and time on the fireline averaged over 9 hours Smoke

exposure was found to be below PELs at these fires, but in some instances it exceeded ACGIH and NIOSH recommendations The authors considered higher exposures to be likely to occur, based on interviews with experienced firefighters and

44

Table 7—Mean smoke exposure at small wildfires in northern California, by

pollutant and work activity

Pollutant

Acrolein (ppm)

Benzene (ppm)

Carbon dioxide (ppm)

Carbon monoxide (ppm)

Formaldehyde (ppm)

Respirable particulate (mg/m3)

Initial attack

0018

0 032

652

120

0 098

1 82

Engine

0015

0 032

546

8 8

0 073

1 91

Mobile attack

n d

0 036

483

12 4

0 051

2 49

Mop up

0010

0015

539

8 8

0 036

1 10
their own observation of missed sampling opportunities Respiratory irritants were the

key health hazard at these fires, although the highest CO exposures measured could

cause adverse health impacts among persons suscept b!e to CO poisoning including

pregnant women and persons with cardiovascular disease Benzene was not a health

hazard among most firefighters but persons working withgasoline containing equip

ment experienced higher benzene exposure Table 8 shows the average and maximum of the TWA exposures among the firefighters

Only three peak exposure samples were obtained in the study These peak expo

sures were below OSHA short-term exposure limits but they could exceed more

stringent exposure limits recommended by ACGIH and NIOSH to protect workers

engaged in hard labor Maximum peak exposures based on nominal 18 minute

samples are shown in table 9

Smoke exposure was highest during strong inversion conditions and when firehnes

were maintained on the downwind edge of burnouts Smoke exposures were higher

during direct attack of spot fires and lower during mop up but insufficient data were

obtained to evaluate the significance of the exposure differences among work activi

ties Atmospheric inversions and ambient windspeed Were considered to be important

variables controlling smoke exposure, but fire-weather gata were not sufficiently representative of local conditions to evaluate the influence of weather

Pollutants were well correlated in smoke, but more high concentration data were

needed to make the correlations useful for predictive purposes This is because there

were so few high-concentration observations that the error bands around the resulting

regressions were especially wide at the higher concentrations where health effects

might be expected, thereby making the estimated exp sures imprecise Electronic carbon monoxide dosimeters were practical devices for roLtine smoke exposure monitoring, but a strong quality assurance program was considered necessary to ensure

valid results The authors recommend a smoke exposure management program that

combines existing safety programs with continued exposure assessment, exposure

management, and risk assessment work

Wildfire Summary Overexposure to CO has been documented during initial attack and in the course of

and Data Needs direct attack activities Respiratory irritants are likely to exceed PELs when CO exposure is high Exposure to smoke at project fires is expected to decline after initial

attack to lower levels during the mop up phase Most measurements of smoke exposure at wildfires have been biased by the inability of researchers to quickly sample

smoke exposure early in the course of a fire At one fire high levels of CO and TPM

were measured in fire camp and were consistent with other measurements on firehnes High smoke exposure can occur anywhere at a fire during inversion conditions

Smoke exposure at fire camps in inversion conditions should be further assessed Exposure to crystalline silica is poorly characterized, but significant exposures are possible during line construction, mop up, and travel through dusty areas when soils have

a crystalline silica component Archived smoke exposure samples should be analyzed

for crystalline silica to better characterize this hazard without the cost of field efforts

45
46

Table 8—Time-weighted average exposures to smoke, Pacific

Northwest, 1992-94

Pollutant

Acrolein (ppm)

Benzene (ppm)

Carbon dioxide (ppm)

Carbon monoxide (ppm)

Formaldehyde (ppm)

Respirable particulate (mg/m3)

Respiratory irritants (no units)

Durationa

Shift

Fire

Shift

Fire

Shift

Fire

Shift

Fire

Shift

Fire

Shift

Fire

Shift

Fire

Mean

0 003

0 004

0016

0 020

439

469

4 1

54

0 023

0 029

0 69

0 90

0 24

0 31

Maximum

0012

0015

0 26

0 36

590

670

32

38

0 079

0 086

23

28

0 79

0 97

Shift = entire workday fire = portion of workday on fireline

Table 9—Peak smoke exposures at large

wildfires in the Pacific Northwest

Pollutant

Acrolein (ppm)

Benzene (ppm)

Carbon dioxide (ppm)

Carbon monoxide (ppm)

Formaldehyde (ppm)

Respirable particulate (mg/m3)

Maximum

0 072

0 058

998

106

0 282

5 5
Among work activities, initial attack by handcrews, engine crews, and mechanized

equipment teams are a high priority for smoke exposure assessment because they

appear most likely to receive high smoke and dust exposures, yet few measurements

exist Differences in exposure potential among fuel types and regions are indicated

because of differences in suppression strategies and residence times of fire in the

fuels Direct-attack fireline construction is a specific activity having moderately high

potential for smoke exposure, but one for which few exposure measurements have

been made Holding during backfiring and burnout operations is another work activity

with few measurements but potentially high smoke exposure potential Mop-up

exposures are likely a concern only in soils with a crystalline silica component or

when residence times of fire are long, such as in regions with heavy ground fuels or

thick duff layers

Fires in the wildland-urban interface are considered to put the firefighter at great risk

of overexposure to smoke because of the need for structure protection, but no exposure measurements have been done when fire was threatening structures Measurements of smoke exposure should be done during structure protection and fire suppression at interface fires Finally, regional differences in smoke exposure are likely

the highest exposures are probably where heavy fuel loading and thick duff layers

predominate, such as Pacific coastal forests, peat bogs in the Great Lakes region

and pocosm fuels in the Southeast

Initial Attack The first firefighters on the scene of a wildfire are responsible for assessing the

incident—evaluating life, property, and resources at risk from the fire, the size and

rate of spread of the fire; and the likelihood of successful control with the suppression

resources at hand The strategy and tactics chosen for initial attack often play a major

role in determining the ultimate size of the fire Because over 95 percent of all wildland fires are kept to small size and are extinguished within the first burning period,

initial-attack actions are overwhelmingly effective Initial attack forces are guided by

the goals of working safely and effectively and achieving control over the fire with a

minimum of suppression costs relative to the resource value at stake Given these

goals, it is reasonable to assume that initial-attack firefighters will exert maximum

effort to contain and extinguish the fire as rapidly as possible This commitment to the

task at hand, while laudable, may cause firefighters to expose themselves to significant smoke during initial attack

At level 5 and level 4 fires, where few firefighters are at the incident, a wide variety of

scenarios are possible Some scenarios have a much higher probability of excessive

smoke exposure than others Common examples are provided from experience and

the literature (Pyne 1984)

Hand crews—An example of a typical incident begins when lightning starts a fire in a

heavily timbered area The local agency dispatches two smokechasers to locate and,

if possible, extinguish the fire. They visually locate the fire and determine that laying

a hose from the nearest road is impractical These firefighters must hike in to the site,

perhaps a burning snag with one-quarter acre of ground fire beneath After sizing it

up, they decide to attempt control themselves, perhaps with backup from a few more

firefighters

47
Firefighters likely would start by "hotspotting" the perimeter where the fire was most

likely to grow beyond their control capabilities This direct attack activity probably has

the highest risk of brief overexposure to smoke The hotspot might be approached

from downhill, upwind, or the blackened area If so, smoke exposure should remain

within recommended ceiling exposure limits But other times, effective direct attack

requires the firefighters to closely flank the fire or approach from the uphill or upwind

side (a safe strategy in this small-fire scenario) This could take an hour or more if

several hotspots are threatening The firefighters' physical effort will probably peak as

they get into the worst smoke, thus intensifying their uptake of pollutants. The firefighters might be able to step out of the smoke to get fresh air, but this often is delayed by excitement and the desire to get the job done Smoke exposure may exceed

ceiling limits and STELs in these situations, especially as the firefighters "pinch off"

the head of the fire or if winds are erratic.

After controlling the immediate threats, the firefighters might turn attention to dropping

a burning snag. An area is prepared and the tree is felled. The firefighters quickly

move into direct attack to prevent the fire from spreading, with concomitant potential

to exceed STELs and ceiling limits. Once the perimeter is established and mop up

begins, it is less probable that any STEL or ceiling exposure limit will be exceeded,

but the cumulative dose of many hours of low-level exposure during mop up combined with the initial direct attack dose could result in exceeding a TWA, even if the

initial attack exposure was within ceiling and STEL limits.

Such direct attack of small fires may provide the greatest opportunity for overexposure

to smoke among firefighters. Local district personnel commonly encounter this type of

fire Smokejumpers and hehtack (helicopter-delivered) and heli-rappel (delivered by

rapelling from a helicopter) crews are other firefighting forces that will experience

similar scenarios Support of hand crews with aerial water and retardant drops can

temporarily quell the fire and allow direct attack of the head of the fire. From a safety

and efficiency perspective, such support can make the difference between effective

suppression versus pulling back and calling for reinforcements. Aerial drops do not

always completely extinguish the fire; the firefighters may be able to finish the direct

attack but might do so while directly downwind of strongly smoldering hotspots

One study reports exposure measurements for handcrews during initial attack, but

only CO exposure was assessed in Western U S fuels Jackson and Tietz (1979)

concluded that the highest COHb levels in nonsmoking firefighters are associated

with initial attack, and these often exceed 5 percent.

Engine-supported attack—Wildland engines (ground tankers) carrying a few firefighters also may experience heavy smoke exposure during their initial attack operations Typically, the engines will approach from an anchor point at the rear of the fire

and move along the flanks using either fixed hoselay or mobile attack, depending on

fuels and terrain. As long as the wind is consistent, the firefighters can stay upwind of

the highly concentrated smoke from the flaming and first smoldering phase of combustion If winds are erratic, they may be exposed to significant amounts of smoke,

but probably for only short periods With small or slow-moving fires, direct control of

flaming areas can put the firefighters in the thick of the smoke, especially when

attacking the head of the fire. Although smoke exposure probably will be brief, the

smoke easily can be concentrated enough to exceed STELs and ceiling limits, and

the firefighter's attention will be focused on the blaze rather than health hazards of

smoke

48
Thus STEL and ceiling exposure limits rather that TWA limits are most likely to be

violated during initial attack If slow-burning heavy fuels or smoldering ground fuels in

the fire perimeter are upwind from the firefighters, these sources contribute to the total

dose received by the firefighters, and this can continue into mop up If smoke exposure approaches STELs during the initial attack, the additional smoke from smoldering

areas can result in violation of TWA exposure limits, even though mop up exposures

are less likely to be hazardous

Only one study reports smoke exposure for crews during initial attack by ground

tankers Reinhardt and others (1995a) found that smoke exposure among engine

crews in grass and chaparral fires was low They noted that the conditions were representative of most fires in that fuel type but did not include the range reported by

experienced firefighters No engine-supported initial-attack measurements are reported in any other fuel types or regions of the United States

Tractor-plow attack—In most of the South and Southeast and parts of the Great

Lakes region, mechanized approaches (bulldozers or a tanker- or tractor-plow) are

employed for initial attack to contain the fire Depending on fire behavior, the attack

may begin at the head or flank of the fire the head is attacked if the rate of spread is

slow The smoke exposure potential any time personnel are downwind of the fire will

be governed by proximity to the fire, windspeed, and drection, and the pollutant

source strength Equipment operators may receive the most smoke exposure at such

fires (Grimes 1994) Because plows or dozers are relatively slow moving, operators

may experience significant smoke exposure when flanking or pinching off the head of

the fire because they cannot get out of the smoke Short-term exposure limits and

ceiling limits are the most likely criteria to be exceeded Where a firefighter follows

behind the plow and burns out (ignites the unburned fuel), hand crews may be used

to hold the plow line during the burnout If winds are sufficient, these firefighters could

experience excessive smoke exposure even though spot fires were not a problem If

fine fuels are dry enough, spot fires during the burnout will necessitate direct control

efforts, which are likely to have high (though short-lived) smoke exposures

Equipment operators may be exposed to high levels ci dust and crystalline silica in

addition to smoke from the fire Hand crews supporting equipment operators also may

receive high exposures during burnout operations and while attacking hot spots Only

one measurement of smoke exposure among mechanized equipment operators

during initial attack is reported in the literature Gnggs and others (1983) found that

one bulldozer operator (also a smoker) had a blood COHb level of 9 percent at a peat

fire in North Carolina

• Few exposure measurements exist among handcrews engine crews, or mechanized forces during initial attack, although data indicate that these situations cause

the highest COHb levels among firefighters Most wldfires are contained as level 4

and 5 fires Data need to be collected at such fires in various fuel types to adequately assess smoke exposure during initial attack

Project Fires Project fires have attracted the most attention among those concerned about smoke

exposure The level 3 through 1 fires involve more acreage, thus fire behavior can be

more extreme through involvement of more fuel, and high rates of heat release can

generate strong winds Firestorms and crown fires have less potential for direct smoke

exposure among firefighters, though, because the crews will be pulling back from

such events The smoke exposure problem at large fires is inherent to specific tasks

and situations, some of which are similar to level 4 or 5 fires and prescribed fires

49
Line construction—Fireline construction may be direct or indirect Direct line construction (hot line) has a much greater chance of significant smoke exposure than

indirect line construction if the fire is actively burning in the area, direct line construction after the smoldering phase is nearly over has little potential for smoke exposure, as does indirect line construction Those involved in burnout of an indirect

parallel line following line completion might experience significant smoke exposure

Direct line construction adjacent to slow-moving fires is more likely to produce

significant smoke exposure if the entrapment risk is low, because firefighters can

confidently work closer to the fire than they would if the fire had a potentially fast rate

of spread Type I crews are most likely to encounter such a hot-line scenario at a

project fire Type II and III crews are not expected to be placed in such situations

For any crew, the main hazard during line construction in dry soils is expected to

be exposure to entrained dust The dust may be composed of large-diameter

particles that do not penetrate the lower respiratory tract, but occupational exposure is regulated nonetheless Many areas of the country have significant levels of

crystalline silica in local soils The presence of crystalline silica in dust lowers the

exposure limit considerably

• Direct-attack fireline construction has a high probability of exposure to smoke,

dust and possibly, crystalline silica Some of the greatest smoke exposures at large

wildfires have been measured during direct-attack activities Additional exposure

measurements are needed during direct attack to expand the variety of fuel types

and fire situations and add respiratory irritants to the CO database

Burnout operations—Burnout operations are similar to prescribed fires in planning

and execution Removing unbumed fuel from the path of the fire during a burnout

operation can result in two groups of exposure hazard among the fire lighters using

hand ignition, and among the fireline holders, when holding is required Aerial ignition

removes the potential for smoke exposure among fire lighters Fire lighters are often

type I crews or experienced type II crews, holders are likely to be type II or III crews

The fire lighters may experience elevated exposure to smoke, especially when winds

are light or variable This is because wind shifts can make it difficult to stay upwind of

the smoke They also may be exposed to benzene if they use drip torches containing

gasoline, but this exposure has not been demonstrated to exceed PELs Based on

sampling from a few wildfires and many prescribed fires, fire lighters usually do not

have significant smoke exposure Anecdotal reports of irritation from fusee smoke are

difficult to evaluate without more data and perhaps specialized sampling

Holders will experience smoke exposure levels ranging between none and high,

depending on the situation Low-exposure situations are foreseen when winds are

favorable for the burning operation or topography prevents smoke from reaching

the holders High smoke exposure potential occurs when winds are unfavorable

or shifting, or when topography or adjacent resources at risk force the holders

to maintain a fireline that the smoke is likely to reach They may be more likely

to receive high smoke exposure if they have a safe escape zone nearby, because

they can manage the backfire with a degree of impunity Functionally, holding line

adjacent to a burnout is equivalent to holding during a prescribed fire If wind or

topography direct smoke across the fireline into the holders, they easily can have

smoke exposures exceeding recommended exposure limits

50
The highest smoke exposures measured in the study by Reinhardt and others

(1995b) were found among a holding crew during a burnout operation Among the

smoke exposures measured in Australia by Brotherhood and others (1990), backfiring operations produced higher smoke exposures than did direct attack line con

struction Smoke exposures were low during one backfire where the firefighters were

downhill from the area burned (Kelly 1992b) but moderate for a brief period during a

second backfire Smoke exposure was highest among a crew lighting and holding

fireline during an exposure assessment (Reh and others 1994) but low in another

crew holding a different flank of the same backfire

• Further exposure assessment is needed among personnel lighting and holding

firehnes during backfires and burnout operations Exposure measurements indicate

that these are high-exposure situations, but few measurements exist

Mop up—Type II and III crews are most often assigned to mop up The predominance of such crews in the workforce means that more firefighters are involved in

mop up than other activities This task is functionally equivalent to mop up at prescribed fires Exposure to significant levels of TPM is more plausible than exposure

to PM3 5 because mop up involves soil and ash disturbances that generate dust

Other respiratory irritants and CO can be present at significant levels, especially so

when there are heavy fuels or duff smoldering in the vicinity Crystalline silica is

another hazard of mop up that is poorly characterized Exposure during mop up may

be a matter of individual work habits, as different firefighters show variations in vigor

of effort and proximity to the source

Some authors found CO exposure during mop up to be low in Western wildfires

(Jackson and Tietz 1979) Other measurements corroborate this (Reh and Deitchman

1992) In a peat fire situation, the smoldering organic layer caused relatively high CO

exposures among those working downwind from the fire (Gnggs and others 1983)

Another study found that mop up during a night shift in inversion conditions had moderate PM3 5 and CO exposure (Harrison and others 1992), but the elevated

exposures may have been caused by the inversion rather than the task One study

found that two peak CO exposures above 200 ppm were associated with mop up

tasks (Materna 1992a) Smoke exposure during mop up was low at small fires in

northern California grass and chaparral (Reinhardt and others 1995a) and relatively

low at large Western U S wildfires (Reinhardt and others 1995b) Crystalline snica

has been identified in PM3 5 samples obtained during mop up by two studies (Kelly

1992a, Materna and others 1992a)

• Mopping up in areas of heavy fuel loading may be associated with moderate smoke

exposure, and a few measurements have quantified crystalline silica exposure in

certain regions of the country Mop up exposure should be further assessed at fires

with heavy fuel loading and areas with thick duff layers Existing PM3 5 sample

filters should be analyzed for crystalline silica and if those results are significant,

additional measurements should be made in different areas of the country

51
Transportation—In many project fires, base camps are located an hour or more (by

vehicle) from the fireline along unpaved roads Although inversion conditions can add

smoke exposure to this transportation time, dust exposure is the most likely problem,

especially so in the dry conditions conducive to large-fire development Crystalline

silica is a potential hazard from some soils Road dust can be controlled by watering

Although measurements are lacking, observations have been made of significant exposures to road dust (Reinhardt 1995) Vehicular exhaust is unlikely to be a significant

source of pollutant exposure, unless firefighters must wait next to idling vehicles The

common task of hiking into the fire along trails and firelines and through blackened

areas is likely to also produce exposure to significant levels of TPM, especially among

large crews Most wildfire smoke exposure assessments have specifically avoided

sampling during transit and, in some cases during hiking to and from the fireline

• Further exposure assessment at large wildfires should specifically sample exposure

to total and respirable particulates during transportation to and from the fireline

Fire camp—Fire camp locations are diverse, but some conditions can create high

smoke exposure in the camp Camp locations are primarily chosen for logistical convenience Proximity to the fire is important to minimize travel time, but this proximity

can cause smoke from the fire to be a problem in camp At large fires, residual smoke

from the fires often impacts the fire camp Down-valley winds at night can transport

smoke into the camp Diurnal inversions are common, occasionally they can keep

smoke trapped in valley bottoms for weeks on end, as observed in the Happy Camp

area of California in 1987 (Sutton and others 1988) Even a typical nightly inversion

can exacerbate the respiratory health of firefighters by exposing them to additional

smoke when they should be recovering from exposure during the previous workshift

Dust-control practices, such as watering high-traffic areas, can minimize the impacts

of vehicular traffic on roads and near camps In the absence of such efforts, TPM

exposure from entrained dust can contribute to the inhalation hazards in fire camps

Exposure to ambient CO can exacerbate fatigue among firefighters seeking rest in

camp Incident command staff often work extended hours planning strategy and managing the fire Although low-level CO exposure should not significantly affect personnel in a fire camp, exposure to moderate levels of CO over extended time could contribute to errors in judgment

Two reports of fire camp smoke exposure are found in the literature. Sampling at the

Happy Camp complex in California measured moderately high dust levels in the fire

camp, and ambient air quality monitoring found dust levels very close to the PEL on

days when inversion conditions existed (Sutton and others 1988) Hourly CO levels in

fire camp were documented at levels above the PEL by the same study. Most fire

camps will not reach such levels, but other measurements also have found CO and

TPM at low to moderate levels in fire camps (Reh and others 1992)

• Additional measurements of CO and respiratory irritants should be obtained in fire

camps when inversion conditions exist

52
Interface Fires

Regional or Specific

Fuel Type Issues

The future of wildland firefighting will be affected by encroachment of human development into locations poorly defensible from wildland fires. Protection of buildings with a

water supply from an engine or standpipe places the wildland firefighter in a difficult

situation Often, the proximity of the structure to the wildland fuels and topographical

limitations are such that ideal firehnes are not possible. In the course of protecting

property from advancing fire, the wildland firefighter may experience significant smoke

exposure (Romey 1994) If a good escape zone is nearby such as a road, the firefighter may not be in physical danger, but relative safety may encourage firefighters

to hold firehnes around structures even though smoke exposure is high Firefighting

within structural interiors is not considered here, as virtually all firefighting agencies

trained in structural firefighting use self-contained breathing apparatus (SCBA) to protect against smoke exposure hazards

Only one study has collected exposure measurements specifically during structure

protection (Kelly 1992a). He found very little smoke exposure because the firefighters

were away ftom the fire This may be the case more often than not but when the fire

finally does arrive, smoke exposure is reported by many to be bad because of the

need to protect property (Stutler 1994) The smoke exposure assessment for initial

attacks in northern California (Remhardt and others 1995a) found relatively low

smoke exposures, but these were small fires in grass and light chaparral fuels and did

not involve structure protection Other parts of the country experiencing urbanization

of wildlands, such as the Great Lakes States, the Southeast, and the Southwest, may

have heavier fuels with correspondingly longer flame residence times in the fuel beds

• Smoke exposure should specifically be assessed at urban interface fires Because

only limited data are available, more representative data need to be collected given

the widespread consensus that these situations can have the worst smoke

exposures.

Many of the considerations mentioned earlier in the 'Wildfire Suppression" section

apply to wildfires as well Here, we summarize the important points from the "Wildfire

Suppression" section and considerations that derive from common suppression tactics

in those fuels

Wildfires in forested areas will have a broad spectrum of smoke exposure controlled

by the residence time of the fire in the fuel, the proximity of the firefighters adjacent

to and downwind of the fire, and atmospheric stability and winds Heavier fuels and

thick duff layers dry enough to support combustion will be associated with the highest

smoke exposures Sparse surface fuels and thin duff and litter layers are associated

with lower smoke exposures

The flammabihty of Southern brushy areas (rough) and Southwestern chaparral during

wildfire season limits smoke exposure when it limits the proximity of the firefighters

When such fires are attacked from the rear, and firefighters advance along the flanks,

smoke exposure should be low (Wachtel 1995) Brief peak exposures are likely the

only concern. Frontal assaults or hotspotting would have more significant exposures,

but STEL compliance would remain the primary concern Burning out of firehnes and

backfiring operations also could cause smoke exposure problems Residence times

are brief in brushy fuels, thus smoke exposure during mop up is probably minor, with

the possible exception of exposure to TPM and crystalline silica

53
Grassland fires have potential smoke exposure among tractor-plow and dozer operators, and those doing line burnout and back-firing operations when spot fires are a

concern Flame residence times are so brief that mop-up exposure is probably inconsequential

In the interior of Alaska, effective direct attack of wildfires in black spruce-feathermoss fuels is often done by swatting the flames with branches or large flaps (similar

to mudflaps from vehicle tires, attached to a handle, also conifer boughs) Brief but

intense smoke exposure may occur during initial attack when this technique is used

(Boatner 1995) Exposure measurements are needed to assess peak exposures

during initial attack When mop up is required in these fuels, smoke exposure can be

extensive (Wilcock 1995)

Peat bog fires and fires in the Southeast pocosin fuels may be among the worst

smoke exposure situations, because the smoldering ground fires could have high

emission factors for products of incomplete combustion (like CO and respiratory

irritants) Wildfires in Florida and southern Georgia swamplands may burn in a similar

manner (Wetzel 1995) The early COHb study in North Carolina (Gnggs and others

1983) found significant levels of smoke during mop up of a peat fire The flaming

phase is brief, similar to other brushy fuels, but because the smoldering phase can

last for weeks or more, mop up can entail extended periods of smoke exposure

(Walden 1995)

• Smoke exposure should be assessed at wildfires in regions with heavy fuel loading

and thick duff layers, such as Pacific Northwest coastal forests, peat bogs in the

Great Lakes region, Alaska taiga, and pocosin fuels in the Southeast

Conclusion and Smoke exposure among firefighters has been recognized as a potential problem since

RGCOmmGndations the early 1970s Several organizations have made efforts to assess smoke exposure

during the last 20 years, with various degrees of success Overall coordination of

these studies has been lacking in the past, and the unfamilianty of occupational health

researchers with the wildland fire workplace and lack of industrial hygiene expertise

among agency fire management personnel have, in some cases, resulted in fragmented, exploratory studies Most of these studies have concluded that they should

be followed with extensive further studies, because it is so difficult to measure such a

variable phenomenon as smoke exposure during firefighting This review has attempted to adequately summarize the findings of the various projects and accurately assess further data needs

Based on exposure monitoring and discussion with fire management experts, exposure to smoke (and dust) among firefighters does not appear to be a problem 90 to

99 percent of the time This is because the tactics of wildfire suppression and prescribed burning have evolved to maximize safety and efficiency and to take advantage

of control opportunities afforded by the environment Nonetheless, in a small percentage of cases, overexposure can occur among firefighters and has been demonstrated

for some components of smoke and dust The long-term health significance of overexposure to smoke is uncertain, but small, statistically significant increases in respiratory symptoms and declines in lung function have been found among firefighters, at

least for several weeks or months Whatever the long-term health risks, overexposure

to CO or respiratory irritants as defined by OSHA or the appropriate state agency is

not acceptable and should be managed further

54
Based on review of the literature and discussions with fire experts, factors contributing

to high smoke exposure include

• A necessity to control the fire with little regard to the inconvenience" of smoke

exposure, examples include prescribed burns and wildfires in the wildland-urban

interface

• The ability to work closely to the fire, as when mechanized equipment provides

good support or when fires are small or rate of spread of the fire is slow and

firefighters can conduct direct attack with little fear of entrapment

• The occurrence of strong smoldering combustion because of a high organic

content of the soil or a heavy ground fuel load, long fire residence time in the

fuelbed causes extended exposure to smoke among suppression and control

forces

• Erratic or strong winds, during initial or direct attack of wildfires and while holding

fireline during burnout operations or prescribed fires

• Poor positioning of firefighters to avoid smoke because of the terrain or adjacent

resources at risk from the fire

• Atmospheric inversion conditions trapping smoke from large fires in topographically

confined spaces.

When one or more of these factors are present, overexposure to smoke will occur

Because of the variability of the fire environment, it is difficult to say how bad the

overexposure will be or among how many firefighters, but the overall percentage of

overexposed firefighters is expected to be low The recommendations for data

collection in the "Wildfire Suppression" and "Wildfire Summary and Data Needs"

sections are aimed at further assessing exposure in such worst case situations

where monitoring has not occurred.

Enough evidence has been gathered to begin to develop and implement smoke exposure management strategies Management plans addressing the possibilities of overexposure indicated by the existing data are not likely to require changes in strategy

as a result of further monitoring, only in the scope of application Agencies interested

in employee health and safety and minimizing liability should press ahead with such

plans and not be frustrated with suggestions for further monitoring Indeed, they

should get used to the concept of routine monitoring and incorporate it (hopefully with

a reduced scope of indicator pollutants) into their exposure management strategies

As OSHA progresses from standards developed in the late 1960s and early 1970s to

comprehensive standards for pollutants, the need for exposure assessment will not

abate, as exemplified by the standard for formaldehyde which requires comprehensive initial monitoring of employees to"

develop a representative sampling strategy and measure sufficient

exposures within each job classification for each workshift to correctly

characterize and not underestimate the exposure of any employee

U S Department of Labor (1994a)

55
Units of Measure

References

Given our discussions with fire experts and reviews of exposure monitoring data, we

believe the additional monitoring recommended should satisfy such requirements

Requirements for initial monitoring are supplemented by periodic monitoring (that is,

every 6 months) as well as monitoring whenever complaints of symptoms associated

with overexposure are received

Because smoke exposure seems to be a problem in only a small percentage of

readily identifiable workshifts, management strategies may have a variety of options

to reduce all exposures to acceptable levels without compromising the effectiveness

of fire management efforts or unreasonably expending limited budgetary resources

When you know.

Meters (m)

Cubic meter (m3)

Miles (mi)

Liters (1)

Milligrams (mg)

Micrograms (μg)

Feet (ft)

Inches (in)

Acres

Multiply by.

3 281

35 32

1 609344

0.908

0.000035274

0 000003527

0.3048

2 54

0.40

To find.

Feet

Cubic feet

Kilometers

Quarts

Ounces

Ounces

Meters

Centimeters

Hectares

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61

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